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2021 Fall Meeting

Materials for energy


Materials for energy applications: hydrogen storage/production, solar cells, super capacitors, thermoelectric & carbon based materials

A symposium dedicated to the wide range of materials with a focused application in the field of renewable and sustainable energy, is much needed which can connect the theory and experimental outcome spontaneously. Our symposium will be one such attempt in the field of energy research.


Due to simple covalent bonding, carbon shows vivid properties, which can be manifested into the energy applications through different dimensionality like carbon quantum dots, fullerene, carbon nanotubes, two-dimensional graphene and Diamond. They all have enormous applications in the field of solar cells, catalysis, batteries, hydrogen production and hydrogen storage. The ongoing feedback between the experiment and theory concerning energy harvesting opens up new direction of scientific thrust not only in the carbon based systems, but also materials that are attaining interesting electronic, structural, optical and transport properties in order to be applied for sustainable energy resolution. Materials modelling have become equally important along with the experimental investigation to predict such properties, which can be tuned in for different energy applications in the area mentioned above. This is because the atomistic insight of a material is one of the intuitive reasons behind its different properties and this insight we can derive from electronic structure of different materials.

The symposium will not only be limited to carbon materials, but also all other novel materials that have attracted the focus of the scientific community in the vast field of energy materials. The applications of such materials will be having a broad view in the area of solar cell, batteries, photocatalytic water splitting,  hydrogen storage and fuel cells. Scientists doing their research in all the above area will be a getting a common platform to showcase their latest findings, which all will be attached through a common string named Energy. The symposium will be a mixture of theory and experiments with a strong view of bridging the gap between them. The choice of materials is having a wide range from oxide materials to recently synthesized transition metal di-chalcogenides and dimension-wise they can be in bulk, surface, monolayer phase or in form of hetero-structures and nano-composits.

Hot topics to be covered by the symposium:

  • Carbon materials of different dimensionalities – present and next generation
  • Application of Diamond in Energy Research
  • Oxide materials and their application in energy research
  • Two-dimensional materials for energy production and storage
  • Perovskite based materials for solar cell
  • Photocatalytic materials for hydrogen production
  • Materials for super Capacitor Technology
  • Thermoelectrics
  • Heterostructured nano-materials and nanocomposits

List of confirmed invited speakers:

  • Zhong Lin (Z.L.) Wang, Georgia Institute of Technology, USA
  • Chris G. Van de Walle, University of California, Santa Barbara, USA
  • Kevin Sivula, EPFL - Ecole polytechnique fédérale de Lausanne, Switzerland
  • Maria Lukatskaya, ETH Zurich, Switzerland 
  • Kourosh Kalantar-zadeh,  University of New South Wales,  Sydney, Australia
  • Wei Luo, Uppsala University, Sweden
  • Maurizia Palummo, University Tor Vergata Rome, Italy
  • Michael Nolan, Tyndall Natl. Institute, Cork
  • Parameswar K. Iyer, Indian Institute of Technology Guwahati, India

Tentative list of scientific committee members:

  • T.W. Kang, South Korea
  • B. Johansson, Sweden
  • C. G.Granqvist, Sweden
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08:20 Welcome message and introduction to the Symposium    
A-1 : Rajeev Ahuja, Uppsala University
Authors : N. Patelli (1), A. Migliori (2), V. Morandi (2), L. Pasquini (1)
Affiliations : (1) Department of Physics and Astronomy, University of Bologna, v.le Berti-Pichat 6/2, 40127 Bologna, IT; (2) Institute for Microelectronics and Microsystems, National Research Council, via Gobetti 101, 40129 Bologna, IT

Resume : The use of Mg as hydrogen storage material is hampered by slow sorption kinetics and high thermodynamic stability. This work reports on biphasic Mg-Ti-H nanoparticles that outperform known Mg-based materials in both respects [1]. By exploiting gas-phase condensation of Mg and Ti vapors under He/H2 atmosphere [2], biphasic nanoparticles are grown, in which the bulk-immiscible MgH2 and TiH2 phases are mixed at the nanoscale. TiH2 conveys catalytic activity for H2 dissociation/recombination and accelerated hydrogen diffusion, while MgH2 provides reversible hydrogen storage. At the remarkably low temperature of 150 °C, hydrogen absorption and desorption are completed in less than 100 s and 1000 s, respectively. Moreover, the equilibrium pressure for hydrogen sorption exhibits a composition-dependent upward shift compared to bulk Mg, resulting in a pressure increase by a factor of about 4.5 in the Ti-richest samples at 100 °C. The enthalpy and entropy of the metal-hydride transformation are both lower in magnitude with respect to the bulk values, suggesting opposite contributions to the free energy of the transformation. The results are analyzed by an interface-induced hydride destabilization model, determining an interfacial free energy difference of 0.38 J/m2 between hydride and metal phases at T=100 °C [1]. These unique composite nanoparticles significantly extend the temperature/pressure window of hydrogen storage applications using Mg-based materials compatible with up-scaling [3]. [1] N. Patelli, A. Migliori, V. Morandi, L. Pasquini, Nano Energy 72, 104654 (2020). [2] N. Patelli, M. Calizzi, A. Migliori, V. Morandi, L. Pasquini, J. Phys. Chem. C. 121, 11166 (2017) [3] L. Pasquini, Energies 13, 3503 (2020)

Authors : Wang Liu, Claudia Zlotea
Affiliations : ICMPE, CNRS

Resume : The downscaling of metal particles to the nanometer range has become an important strategy for the design of new materials for many applications, such as hydrogen storage and heterogeneous catalysis. Downsizing the metal particles to nanometers can introduce fundamental changes compared to the corresponding bulk state.[1,2 ] Among the noble metals, Pd is the only metal that absorbs hydrogen and forms a hydride at ambient temperature and pressure. Therefore, Pd-hydrogen bulk system has been well studied and understood.[3] The purpose of this work is to study the nanosize effect on the hydrogen absorption/desorption into a series Pd nanoparticles supported on porous carbon with average size 1.4, 2.0 and 6.0 nm. The Pd nanoparticles were prepared by a wetness impregnation method followed by reduction under H2/Ar flow at different temperatures. The physico-chemical properties of the materials were characterized by X-ray diffraction, transmission electron microscopy and N2 adsorption. The hydrogen sorption properties were studied by in situ XRD, in situ X-ray absorption spectroscopy (XAS), pressure-composition-isotherm (PCI) and thermo desorption spectroscopy (TDS) measurements. At room temperature and pressure, the miscibility gap between solid solution (α phase) and hydride phase (β phase) narrows by decreasing the Pd nanoparticle size until the absence of any phase transition for 1.4 nm nanoparticles. Absorption and desorption show only partial reversibility for Pd nanoparticles at low pressures, contrary to bulk. These non-closing absorption/desorption PCI curves suggest that H is trapped inside nanoparticles. This is confirmed by the variation of the nearest neighbour distance RPd-Pd under 1 bar H2 (absorption) and 1 bar He (desorption) by EXAFS refinements (Figure 1B). We demonstrated that H trapping in Pd nanoparticles (irreversible part) is size-dependent: smaller the size, larger the amount of trapped H. Moreover, DFT calculations seem to indicate that these strong H trapping sites are located in the subsurface of nanoparticles. (1) Pundt, A. Hydrogen in Nano-Sized Metals. Adv. Eng. Mater. 2004, 6 (12), 11–21. (2) Bérubé, V.; Radtke, G.; Dresselhaus, M.; Chen, G. Size Effects on the Hydrogen Storage Properties of Nanostructured Metal Hydrides: A Review. International Journal of Energy Research 2007, 31 (6–7), 637–663. (3) Oates, W. A. Thermodynamic Properties of the Pd-H System. Journal of the Less Common Metals 1982, 88 (2), 411–424.

Authors : Celia Mª Rueda (1), Arianna Melillo (1), Cristina Vallés-García (1), Belén Ferrer (1), Herme G. Baldoví, (1) Sergio Navalón(1)
Affiliations : (1) Universitat Politecnica de Valencia, Spain

Resume : Metal organic frameworks (MOFs) are porous and crystalline materials constituted by the coordination of metal clusters to organic ligands.[1] In the last years MOFs have found application as photocatalysts for the production of solar fuels.[2] In particular, a vast number of studies have shown the possibility to produce hydrogen using MOFs as photocatalysts in the presence of sacrificial electron donors such as methanol. One important step forward in the use of MOFs has been their use as multifunctional photocatalysts where two or more active sites catalyze different elementary steps of the reaction. In the present work we report the use of UiO-66(Zr)-NH2 as bifunctional and reusable photocatalyst for the reduction of p-nitrophenol to p-aminophenol in the presence of methanol. This tandem reaction occurs via photocatalytic hydrogen generation from a water/methanol mixture in the first step and then a reduction of p-nitrophenol to p-aminophenol in the Frustrated Lewis acid-base present in the defective metal nodes of the MOF. The catalytic activity of UiO-66(Zr)-NH2 is higher than that of UiO-66(Zr)-X (X: H or NO2) or MIL-125(Ti)-NH2. Catalytic experiments showed that the presence of NO2 as electron withdrawing group enhanced molecular H2 activation and p-nitrophenol reduction under dark reaction conditions. The higher activity of UiO-66(Zr)-NH2 as bifunctional catalyst attributed to its more negative LUCO reduction potential and enhanced visible light absorption due to the presence of the amino group in the terephthalate organic ligand of the MOF. The advantage of this tandem photocatalytic H2 generation–catalytic hydrogenation would be that no H2 gas is needed, and the process is controlled by on–off switching of light.

Authors : Ou Jin(1), Astrid Pundt(1), Dorothée Vinga Szabó(1), Stefan Wagner(1), Claudio Pistidda(2), Yuanyuan Shang(2)
Affiliations : (1) Institute for Applied Materials – Materials Science and Engineering, Karlsruher Institut für Technologie, Germany (2) Institute of HydrogenTechnology, Helmholtz-Zentrum Geesthacht, Germany

Resume : The detrimental environmental footprints caused by fossil fuel and its foreseeable shortage in the future have promoted the development and research of renewable energy sources. As a clean and reproducible energy carrier, hydrogen can store and deliver a large amount of energy. For the extensive application of hydrogen, the development of advanced hydrogen storage materials becomes vital. Reactive Hydride Composites (RHCs) have been studied intensively due to their exceptional hydrogen storage capacity and enhanced reversibility [1], which were initially derived from light metal complex hydrides (e.g., LiBH4, LiNH2, NaAlH4) in combination with a second hydride (e.g., LiH, MgH2) [2-4]. Among various RHCs, the LiBH4-MgH2 composite exhibits a far larger hydrogen storage capacity of ~ 12 wt% of hydrogen especially compared to the traditional storage methods, e.g., compression and liquefaction [5]. With the decreased standard reaction enthalpy down to ~ 45 kJ/mol H2, the decomposition of the LiBH4-MgH2 composite already occurs at ~ 170 °C under automorphic pressure from the thermodynamic point of view [4]. Due to these prominent hydrogen storage properties, the LiBH4-MgH2 composite is regarded as one of the most competitive candidates for both mobile and stationary applications in the future, according to the International Energy Agency Task 22 [6]. However, as other RHCs, the commercial applications of the LiBH4-MgH2 composite are enormously limited by the sluggish kinetic behavior, which is primarily ascribed to the nucleation limit of MgB2 during decomposition [7]. In practice, it takes almost 30 hours to fully discharge hydrogen from the composite at 400 °C under hydrogen backpressure of 5 bar [8]. To overcome this restriction, it was proposed that the transition metal-based additives can facilitate the formation of MgB2 and therefore accelerate the decomposition process of the LiBH4-MgH2 composite [7]. However, the role of the additives in the decomposition path was still not fully revealed. To unravel the mechanism of the additive impact, as well as the kinetic restriction, the LiBH4-MgH2 composite in the presence and absence of 3TiCl3•AlCl3 was observed in this work. Utilizing versatile transmission electron microscopy (TEM) techniques, the MgB2 crystals generated after decomposition of the LiBH4-MgH2 composite are emphatically studied. According to the TEM results, it was observed that the morphology of the reaction products after decomposition of the LiBH4-MgH2 composite is changed by adding 20 mol% 3TiCl3•AlCl3 additives. Based on the varied morphologies, two distinct geometries of the MgB2 crystals have been distinguished: one is bar-like, the other is plate-like. Via 4D-STEM, the crystallographic orientations of these MgB2 bars and plates concerning their geometric shapes have been determined to be the same, which are <1-210>, <10-10>, and <0002>. Furthermore, the generated Mg grains from the decomposition of MgB2 and the formed TiB2 nanoparticles coming from the additives are identified to be the precursors, which facilitate the nucleation and growth of MgB2 bars and MgB2 plates, respectively. Since no optimal interface between the precursors and the MgB2 phase exist in the experiments, their orientation relationships cannot be determined in a conventional way by focusing on their interface. For this reason, the edge-to-edge matching model [9-12] was applied to analyze their orientation relationships, which are related to the heterogeneous nucleation of the MgB2 phase based on the varied precursors (Mg and TiB2). It was also found that the size of Mg grains is much larger than the width of MgB2 bars, whereas the size of TiB2 nanoparticles is smaller than the width of MgB2 plates. This discrepancy indicates the varied growth behavior for MgB2 bars and MgB2 plates after nucleation. In combination with their crystallographic characteristics, the one-dimensional growth along <1-210> for MgB2 bars and the two-dimensional growth along <1-210> and <10-10> for MgB2 plates are expected. In principle, the different growth behavior for MgB2 can be likely ascribed to the large distinction of the precursor size between Mg and TiB2, which will induce the strain energy to different extents. In other words, not only the MgB2 nucleation but also the growth is affected by the precursors. From this perspective, the varied nucleation and growth behavior of the MgB2 phase in the decomposition of LiBH4-MgB2, which is altered by additives and also nanoconfinement [13], can be consistently explained. This new knowledge should contribute to understanding the MgB2 nucleation and growth process in the LiBH4-MgB2 composite and facilitate the design of more effective additives, which should match well with the MgB2 phase from the crystallographic point of view. On the other hand, since the precursor size seems to play a tremendous role not only in the MgB2 nucleation process but also in the growth process, controlling the precursor size should be further emphasized. Reference 1. Milanese, C., et al., Complex hydrides for energy storage. international journal of hydrogen energy, 2019. 44(15): p. 7860-7874. 2. Chen, P., et al., Interaction between lithium amide and lithium hydride. The Journal of Physical Chemistry B, 2003. 107(39): p. 10967-10970. 3. Barkhordarian, G., et al., Unexpected kinetic effect of MgB2 in reactive hydride composites containing complex borohydrides. Journal of Alloys and Compounds, 2007. 440(1-2): p. L18-L21. 4. Vajo, J.J., et al., Thermodynamic destabilization and reaction kinetics in light metal hydride systems. Journal of Alloys and Compounds, 2007. 446: p. 409-414. 5. Puszkiel, J.A., Tailoring the kinetic behavior of hydride forming materials for hydrogen storage, in Gold nanoparticles-reaching new heights. 2018, IntechOpen London, UK. 6. Hauback, B.C. Task 22 of IEA HIA _ Fundamental and Applied Hydrogen Storage Materials Development. in 18th World Hydrogen Energy Conference 2010 - WHEC 2010. 2010. 7. Bösenberg, U., et al., Role of additives in LiBH4–MgH2 reactive hydride composites for sorption kinetics. Acta Materialia, 2010. 58(9): p. 3381-3389. 8. Bösenberg, U., et al., Hydrogen sorption properties of MgH2–LiBH4 composites. Acta Materialia, 2007. 55(11): p. 3951-3958. 9. Zhang, M.-X. and P. Kelly, Edge-to-edge matching model for predicting orientation relationships and habit planes—the improvements. Scripta Materialia, 2005. 52(10): p. 963-968. 10. Zhang, M.-X. and P. Kelly, Edge-to-edge matching and its applications: Part II. Application to Mg–Al, Mg–Y and Mg–Mn alloys. Acta materialia, 2005. 53(4): p. 1085-1096. 11. Zhang, M.-X., et al., Crystallographic study of grain refinement in aluminum alloys using the edge-to-edge matching model. Acta Materialia, 2005. 53(5): p. 1427-1438. 12. Kelly, P. and M.-X. Zhang, Edge-to-edge matching—The fundamentals. Metallurgical and Materials Transactions A, 2006. 37(3): p. 833-839. 13. Gosalawit–Utke, R., et al., Effective nanoconfinement of 2LiBH4–MgH2 via simply MgH2 premilling for reversible hydrogen storages. International journal of hydrogen energy, 2014. 39(28): p. 15614-15626.

Authors : Yuanyuan Shang1, Thi Thu Le1, Ou Jin2, Claudio Pistidda1*, Astrid Pundt2, Thomas Klassen1, 3, Martin Dornheim1*
Affiliations : 1 Institute of Hydrogen Technology, Helmholtz-Zentrum hereon GmbH, Max-Planck-Straße 1, 21502 Geesthacht, Germany 2 Karlsruhe Institute of Technology (KIT), Institute of Applied Materials (IAM-WK), Engelbert-Arnold-Straße 4, 76131 Karlsruhe, Germany 3Helmut Schmidt University/University of the Federal Armed Forces, Holstenhofweg 85, 22043 Hamburg, Germany *Correspondence to:,

Resume : A systematic investigation into the effect of TM-based additives on the dehydrogenation properties of the reactive hydride composite (RHC) 2NaBH4+MgH2 is herein reported. The material doped with 3AlCl3AlCl3 exhibits superior dehydrogenation kinetics, particularly the second dehydrogenation step, compared to the pristine system. The addition of 3AlCl3AlCl3 also triggers the change of the reaction mechanism of the second dehydrogenation step from a two-dimensional interface controlled growth to a two-dimensional growth of existent nuclei at a constant interface rate. These differences are attributed to the in-situ formation of nanostructured TM-based phases, which act as heterogeneous nucleation sites for MgB2. The microstructural investigation carried out on the dehydrogenated 2NaBH4+MgH2 via high-resolution transmission electron microscopy (HRTEM) shows significant differences in the MgB2 morphology formed in the doped and undoped system.

Authors : Michael Sachs,1 Hyojung Cha,1 Jan Kosco,2 Catherine M. Aitchison,3 Laia Francàs,1 Sacha Corby,1 Chao-Lung Chiang,4 Anna A. Wilson,1 Robert Godin,1 Alexander Fahey-Williams,1 Andrew I. Cooper,3 Reiner Sebastian Sprick,3 Iain McCulloch2,1 and James R. Durrant1
Affiliations : 1 Department of Chemistry and Centre for Plastic Electronics, Imperial College London, U.K.; 2 Department of Physical Sciences and Engineering, KAUST Solar Centre (KSC), Saudi Arabia; 3 Department of Chemistry and Materials Innovation Factory, University of Liverpool, U.K.; 4 National Synchrotron Radiation Research Center, 101 Hsin-Ann Rd., Hsinchu 30076, Taiwan

Resume : Due to the intermittency of sunlight there is a growing interest in harnessing solar energy for the synthesis of sustainable fuels. While inorganic materials have primarily been used for this purpose, organic semiconductors are currently gaining substantial momentum for application as photocatalysts - particularly due to their much higher synthetic flexibility. For instance, their optical band gap can be tuned throughout large parts of the solar spectrum by copolymerizing selected monomers in defined ratios. This tunability has sparked intense research interest in organic photocatalysts,[1] however, the fundamental understanding of photoinduced processes in these systems and the characterisation of their catalytically active sites have stayed behind the rapid development of new materials. In this presentation, I will demonstrate how transient and operando optical spectroscopic techniques can be used to track the evolution of photogenerated reaction intermediates in polymer photocatalysts on timescales of femtoseconds to seconds after light absorption: short laser pulses are used to study these photocatalysts under transient conditions whereas long LED pulses are employed to establish operando catalytic conditions, and reaction intermediates are then probed optically. In this way, photogenerated charge yields can be compared between materials to understand differences in their hydrogen evolution activity,[2] and the transfer of photogenerated electrons to catalytically active sites can be monitored.[3] To illustrate these points, I will draw direct comparisons between nanoparticle photocatalysts made from the polymers F8BT, P3HT, and the dibenzo[b,d]thiophene sulfone homopolymer, P10, which is one of the most performant polymer photocatalysts reported to date.[2] References [1] Wang, Y.; Vogel, A.; Sachs, M.; Sprick, R. S.; Wilbraham, L.; Moniz, S. J. A.; Godin, R.; Zwijnenburg, M. A.; Durrant, J. R.; Cooper, A. I.; et al. Current Understanding and Challenges of Solar-Driven Hydrogen Generation Using Polymeric Photocatalysts. Nat. Energy 2019, 4 (9), 746–760. [2] Sachs, M.; Sprick, R. S.; Pearce, D.; Hillman, S. A. J.; Monti, A.; Guilbert, A. A. Y.; Brownbill, N. J.; Dimitrov, S.; Shi, X.; Blanc, F.; et al. Understanding Structure-Activity Relationships in Linear Polymer Photocatalysts for Hydrogen Evolution. Nat. Commun. 2018, 9 (1), 4968. [3] Sachs, M.; Cha, H.; Kosco, J.; Aitchison, C. M.; Francàs, L.; Corby, S.; Chiang, C.-L.; Wilson, A. A.; Godin, R.; Fahey-Williams, A.; Cooper, A. I.; Sprick, R. S.; McCulloch, I.; Durrant, J. R. Tracking Charge Transfer to Residual Metal Clusters in Conjugated Polymers for Photocatalytic Hydrogen Evolution. J. Am. Chem. Soc. 2020, 142 (34), 14574–14587.

10:30 Q&A live session / Break    
A-2 : Rajeev Ahuja, Uppsala University
Authors : Oluwagbemiga P. Ojo (1), Wilarachchige D. C. B. Gunatileke (1), Hsin Wang (2), George S. Nolas (1)
Affiliations : (1) Department of Physics, University of South Florida, Tampa, FL, 33620, USA. (2) Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.

Resume : Due to the growing need for clean and renewable energy, the discovery of new thermoelectric materials with tunable transport properties is of current interest. A relatively unexplored class of quaternary chalcogenides of the type I-II2-III-VI4, where I = Cu or Ag, II = Zn or Cd, III = Al, Ga or In, and VI = S, Se or Te with multiple compositions primarily consisting of earth abundant and non-toxic constituent elements, all with the sphalerite structure were studied and their structure-property relationships investigated. The temperature dependent electrical and thermal properties were investigated as a function of doping, metal content and stoichiometry. An insulator-to-semiconductor transition with excess Cu was observed for these p-type materials. Thermal conductivity data indicated that these quaternary chalcogenides possess intrinsically low thermal conductivity, an important property for thermoelectrics, and attributable to the specific bonding these materials possess. Our work shows the potential for optimization that, in addition to the intrinsically low thermal conductivity, provides a basis for research towards thermoelectrics applications.

Authors : Wilarachchige D. C. Bhagya Gunatilleke, George S. Nolas
Affiliations : University of South Florida, Tampa FL, USA

Resume : In achieving high ZT (the dimensionless thermoelectric figure of merit) chalcogenides, investigating the mechanisms that lower the thermal conductivity plays an important role. However, understanding the structural attributes that result in low thermal conductivity in ternary and quaternary chalcogenides is still in need of attention. Temperature dependent thermal properties of certain ternary and quaternary chalcogenides, including new compositions that have not previously been studied, were investigated to advance this goal. The underlying structural features that affect the thermal properties of these materials are discussed by analyzing their effect on thermal conductivity and specific heat. Using the Debye-Callaway model in investigating the thermal properties, various phonon scattering mechanisms for these materials were investigated. For example, the dynamic disorder due to distorted CuSe4 tetrahedra in BaCdSnSe4 and BaCu2SnQ4 (Q = S, Se) results in resonance scattering of phonons while alloying resulted in further decreasing the thermal conductivity. Soft modes in BaCdSnSe4 give rise to large dynamic disorder thus lowering the thermal conductivity of this material. In addition to the complex crystal structure with many atoms in the unit cell, the stereochemically active lone-pair electrons in Cu4Bi4Q9 (Q = S, Se) resulted in very low thermal conductivity values. These findings were corroborated by the Einstein and Debye temperatures obtained from our experimental data. Complex lattice vibrations due to the large unit cells as well as various structural features due to the specific structure types in these materials result in an increase in optical modes that affect the thermal conductivity in these materials, and lead to further suppression of the thermal conductivity in certain materials. The investigation of various phonon scattering mechanisms that affect the thermal properties and give rise to low thermal conductivity contributes to the fundamental understanding of these materials. Together with tuning of the electrical properties, these results can be employed towards optimization of the thermoelectric properties of ternary and quaternary chalcogenides as they continue to be of interest for thermoelectrics applications.

Authors : Abhishek Ghosh, Mujeeb Ahmad, Prashant Bisht, Bodh Raj Mehta
Affiliations : Indian Institute of Technology Delhi

Resume : Enhancement in the thermoelectric (TE) properties through carrier filtering in polycrystalline Sb2Te3 thin film is realized by incorporating size-selected Au nanoparticles grown by an integrated gas-phase synthesis method. Crystalline Singlet nanoparticles of Au having a narrow size distribution are embedded between two Sb2Te3 layers. Thermoelectric properties have been investigated by varying the concentration of nanoparticles, which reveal a significant increase in the Seebeck coefficient and power factor with a slight deterioration in electrical conductivity. Samples containing non-size selected Au particles with broad size distribution are also synthesized to understand the effect of non-uniformity on TE properties. Scanning probe techniques were employed to understand the nature of the interface formed between Sb2Te3 and Au nanoparticles. The study provides an opportunity to manipulate the TE properties in Sb2Te3 thin films through designing a metal-semiconductor heterostructure by controlling the concentration and randomness to achieve a high TE performance.

Authors : Arnab Majumdar1,2, Suman Chowdhury3, Rajeev Ahuja1,4
Affiliations : 1 Department of Physics and Astronomy, Box 516, Uppsala University, Uppsala, SE-75120, Sweden 2 Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C. P. 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada 3 Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, 3 Nobel Street, Moscow 121205, Russia 4 Department of Physics, Indian Institute of Technology Ropar, Rupnagar 140001, Punjab, India

Resume : A myriad of two-dimensional chalcogenide materials has become quite popular in the recent past for their promising thermoelectric properties. The thermoelectric performance of materials improves on stepping down along the physical dimensionality of the system. Two-dimensional hexagonal of GaX, InX, and TlX (X = S, Se and Te) have already been studied extensively in the literature. In the phases reported in the literature, the group-13 non-chalcogen atoms occupy the two inner planes while the chalcogens occupy the two outer planes of the unit cell. In this work, we have proposed the opposite arrangement. That is the chalcogen atoms occupy the two inner planes while the Ga/In/Tl atoms occupy the two outer planes of the unit cell. This leads to ultralow thermal conductivity which eventually results in superior thermoelectric performance. In this work we have studied in detail the thermoelectric properties of hexagonal AX (A= Ga, In & Tl, X = S, Se & Te) monolayers and compare the results having both the atomic arrangements. The very low lattice thermal conductivity of our new proposed atomic arrangement is due to the outermost valence s-orbital lone pair of the chalcogens which leads to enhanced anharmonicity. Furthermore, the enhanced anti-crossing of the phonon branches as well leads to lower lattice thermal conductivity. The electronic, dynamical, thermodynamical, and elastic properties have also been studied. We think that these results should have a significant impact on the synthesis of high-performance thermoelectric materials based on chalcogenides of gallium, indium, and thallium.

Authors : Vázquez-López, A.*(1), Bartolomé, J.(1, 2), Ramírez-Castellanos, J.(3) Maestre, D.(1) & Cremades, A.(3).
Affiliations : (1) Dpt. Física de Materiales, Fac. CC Físicas, Universidad Complutense de Madrid, Spain (2) Dpt. Física Aplicada, Fac. Ciencias, Universidad Autónoma de Madrid, Spain (3) Dpt. Química Inorgánica, Fac. CC Químicas, Universidad Complutense de Madrid, Spain * lead presenter

Resume : Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) has been stablished as a potential polymer in different fields of research, such as solar cells, thermoelectrics and gas sensing. However, the use of pristine PEDOT:PSS is hindered due to its poor conductivity (σ~0.1-10 Scm-1) and limited Seebeck coefficient (~12 μVK-1), which can be overcome by different approaches such as the addition of solvents and/or nanoparticles. In this work, Ethylene glycol (EG) and SnO nanoparticles (SnO-nps) synthesized by hydrolysis have been added to PEDOT:PSS in order to fabricate hybrid composites with improved functionality in gas sensing and thermoelectric devices. SnO is one of the few p-type semiconductor oxide with unique properties, but still remains under-explored due to its inherent metastability and natural oxidation to SnO2, which can be limited by using SnO-nps embedded in a polymeric matrix. Herein we report on the assembly of PEDOT:PSS/SnO based composites. Different samples containing SnO or/and EG in variable concentrations have been deposited onto glass substrates via spin coating. Composites with 1% wt SnO-nps and EG show improvement on the thermoelectric power factor from 0.007 to 0.23 μWm-1K-2, as compared with pristine PEDOT:PSS. Besides, these hybrid composites used as gas sensor show an improvement on their sensitivity to ethanol, by a factor of 2.5.

Authors : Shantanu Misra, Bartlomiej Windlocha, Anne Dauscher, Bertrand Lenoir, Christophe Candolfi
Affiliations : Shantanu Misra (Institut Jean Lamour, UMR 7198 CNRS – Université de Lorraine, 2 allee Andre Guinier – Campus ARTEM, BP 50840, 54011, Nancy Cedex, France); Bartlomiej Windlocha (AGH University of Science and Technology, Faculty of Physics and Applied Computer Science – Al. Mickiewicza 30, 30-059 Krakow, Poland); Anne Dauscher (Institut Jean Lamour, UMR 7198 CNRS – Université de Lorraine, 2 allee Andre Guinier – Campus ARTEM, BP 50840, 54011, Nancy Cedex, France); Bertrand Lenoir (Institut Jean Lamour, UMR 7198 CNRS – Université de Lorraine, 2 allee Andre Guinier – Campus ARTEM, BP 50840, 54011, Nancy Cedex, France); Christophe Candolfi (Institut Jean Lamour, UMR 7198 CNRS – Université de Lorraine, 2 allee Andre Guinier – Campus ARTEM, BP 50840, 54011, Nancy Cedex, France)

Resume : Over the last few decades, researchers have been constantly able to improve the dimensionless thermoelectric figure of merit, ZT, that governs the efficiency of the thermoelectric devices through different routes concerning improvement of power factor, decreasing of lattice thermal conductivity or synergistic effect of both these points. One possible way of optimizing the power factor of semiconductors is through the introduction of an impurity that gives rise to a resonant level (RL) at the edge of either the valence or conduction bands [1,2]. The impurity atoms distort locally the electronic band structure beyond the rigid-band model. A significant increase in the thermopower and, hence, in the power factor is observed when the chemical potential resides in this distortion due to the increased Density of States (DOS). So far, the main experimental strategy to unravel the resonant nature of an impurity in semiconductor was tied to the variation of the thermopower as a function of the charge carrier concentration, known as the Ioffe-Pisarenko plot. However, as we discuss in our work, Pisarenko plot remains inconclusive in many practical cases, since the dopant introduced to the semiconductor may change the thermopower of the material due to many different effects, and it is not possible to conclude on the resonant or non-resonant character of the impurity by analyzing only the Pisarenko plot. Hence, in this work, we propose a novel method which allows to distinguish between resonant and non-resonant impurities in semiconductors. Using a combination of experimental data and theoretical calculations based on the Kubo-Greenwood formalism, we show that an analysis of the low-temperature electrical resistivity and carrier mobility allows to unambiguously conclude on the character of a given impurity, even when the Ioffe-Pisarenko plot of thermopower is inconclusive. Our findings are based on a detailed analysis on the canonical SnTe system doped with resonant In[3]. References 1. Heremans, J. P., Jovovic, V., Toberer, E. S., Saramat, A., Kurosaki, K., Charoenphakdee, A., Yamanaka, S. & Snyder, G. J. Enhancement of Thermoelectric Efficiency in PbTe by Distortion of the Electronic Density of States. Science 321, 554 (2008). 2. Heremans, J. P., Wiendlocha, B. & Chamoire, A. M. Resonant levels in bulk thermoelectric semiconductors. Energy Environ. Sci. 5, 5510 (2012). 3. Wiendlocha, B., Misra, S., Dauscher, A., Lenoir, B. & Candolfi, C. Residual resistivity as an independent indicator of resonant levels in semiconductors. Mater. Horiz. (2021). doi:10.1039/D1MH00416F

Authors : Mariana Rocha, Margarida Maia, André Pereira
Affiliations : Mariana Rocha - IFIMUP – Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal; Margarida Maia - IFIMUP – Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal; André Pereira - IFIMUP – Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal

Resume : During the past few decades, with rapid enlargement of human society, consumption of traditional energy has increased exponentially. Thermoelectric materials (TE) can generate electrical energy when they are exposed to a thermal gradient, considered one of the most important solutions for sustainable energy harvesting.[1,2] These materials present lightweight, small size, pollution free and recycling potential.[2] One of the most used TEs is the alloy Bi2Te3 since it is considered as the best performing thermoelectrical material near room temperature (150-300 K).[2] The performance of a thermoelectric material is assessed by a dimensionless figure-of-merit, zT, defined as zT = S2σT/(κe + κl), where S, σ, κe, κl and T are the Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, and the absolute temperature, respectively. An average zT between 1.5–2 can enable substantial waste-heat harvesting and application in primary power generation.[3] Recently, in order to obtain high zT values, was developed Bi2Te3 nanomaterials leading thus a strong quantum confinement and a significant reduction of the lattice thermal conductivity, causing an increase of the zT value.[4] Herein, it was prepared Bi2Te3 NPs using a chemical reduction process and a polyol to confine the NPs size.[5] The NPs were characterized by XRD, DLS, SEM and transport properties presenting a mix of Bi2Te3 with a small amount of Te, an average hydrodynamic diameter of 261±23 nm (PDI = 0.31±0.04, n = 5), S = +172.8 µV K-1 (being p-type material), σ = 22.20 S mm-1, and a Power Factor of 0.662 µW m-1 K-2. Acknowledgements: This work was funded by H2020-EU.1.2.1. - FET Open Project (WiPTherm, grant agreement ID: 863307). References: [1] P. Srivastava and K. Singh, Bull. Mater. Sci., 2013, 36, 765–770. [2] M. M. Rashad, A. El-Dissouky, H. M. Soliman, A. M. Elseman, H. M. Refaat and A. Ebrahim, Mater. Res. Innov., 2017, 22, 1–9. [3] T. Nakamoto, S. Yokoyama, T. Takamatsu, K. Harata, K. Motomiya, H. Takahashi, Y. Miyazaki and K. Tohji, J. Electron. Mater., 2019, 48, 2700–2711. [4] Y. Xu, Z. Ren, W. Ren, G. Cao, K. Deng and Y. Zhong, Mater. Lett., 2008, 62, 4273–4276. [5] K. Kim, H. M. Lee, D. W. Kim, K. J. Kim, G. G. Lee and G. H. Ha, J. Korean Phys. Soc., 2010, 57, 1037–1040.

Authors : Tim Freund, Peter Wellmann
Affiliations : Friedrich-Alexander Universität Erlangen-Nürnberg, Institute of Materials for Electronics and Energy Technology; Friedrich-Alexander Universität Erlangen-Nürnberg, Institute of Materials for Electronics and Energy Technology

Resume : Chalcogenide Perovskites are a novel class of semiconductors that have been proposed as solar cell materials. However, few processing routes have been established for the synthesis of thin films based on those compounds. [1] The most commonly found one uses the respective Oxide as a base material, which is sulfurized to obtain the desired product. [2-4] Co-sputtering followed by rapid thermal processing [5] or spin coating of colloidally stabilized powders are techniques used by other groups. [6] In our work, we are utilising BaS3, which possesses a relatively low melting point compared to other compounds from this system, for the synthesis of BaZrS3 thin films. Therefore, our approach loosely follows the stacked layer processing commonly used for the fabrication of Cu(In,Ga)Se2 solar cells and similar materials in that our precursor layers are sequentially deposited upon a substrate and subsequently annealed to form the desired product. In our approach, BaS is first deposited upon the substrate and then sulfurized to form BaS3. Then, elemental Zirconium is deposited on this film and a final annealing step is applied to obtain the desired material. Based on the preliminary work to synthesize BaS3, we report on the phase formation mechanisms of BaZrS3 based on high temperature annealing of stacked layers of BaS3 and Zr at temperatures up to 1600°C. 1. Sun, Y.Y., et al., Chalcogenide perovskites for photovoltaics. Nano Lett, 2015. 15(1): p. 581-5. 2. Shaili, H., et al., Synthesis of the Sn-based CaSnS3 chalcogenide perovskite thin film as a highly stable photoabsorber for optoelectronic applications. Journal of Alloys and Compounds, 2021. 851. 3. Gupta, T., et al., An Environmentally Stable and Lead-Free Chalcogenide Perovskite. Advanced Functional Materials, 2020. 30(23): p. 2001387. 4. Pandey, J., et al., Local ferroelectric polarization in antiferroelectric chalcogenide perovskite BaZrS3 thin films. Physical Review B, 2020. 102(20). 5. Comparotto, C., et al., Chalcogenide Perovskite BaZrS3: Thin Film Growth by Sputtering and Rapid Thermal Processing. ACS Applied Energy Materials, 2020. 3(3): p. 2762-2770. 6. Ravi, V.K., et al., Colloidal BaZrS3 Chalcogenide Perovskite Nanocrystals for Thin Film Device Fabrication. Nanoscale, 2021.

13:00 Q&A live session / Break    
A-3 : Wei Luo, Uppsala University
Authors : Alexander W. Stewart, Bernabé Marí Soucase, Amal Bouich
Affiliations : Universitat Politècnica de València (IDF)

Resume : CsPbIBr2 films have been identified as prime candidates for use as top cells in tandem devices, however their inherent long-term instability inhibits their large-scale commercialization. By quenching CsPbIBr2 with isopropanol while it was being spin-coated, we synthesized films with extended lifespans and improved crystallinity. The crystallinity and stability of the films was quantified using a combination of FESEM images, x-ray diffraction, photoluminescence, absorbance measurements. The time during the spin programme in which the antisolvent was applied was varied between 5 to 20 seconds, leading us to conclude that a period of 10 seconds gives the best results. Our champion film showed exceptional stability, since after it was exposed to air for 5 weeks it still outperformed the freshly prepared reference sample which had no antisolvent applied to it. Our results suggest that the application of isopropanol, 10 seconds after the spin-programme commences, is a simple and reproducible way to significantly enhance CsPbIBr2 films.

Affiliations : Senior Lecturer, Lead PV and optoelectronic lab. Renewable Energy Systems School of Water, Energy and Environment Building 52, Cranfield University, Cranfield, Bedfordshire MK43 0AL

Resume : The presence of toxic lead makes large-scale manufacturing of perovskite solar cells challenging due to legislation and environment issues. In this talk we will discuss our research work on the development of less-toxic and more sustainable MBI (CH3NH3)2Bi2I9)) perovskite solar cells with detailed spectroscopic and optoelectronic characterization.2-4 The talk will showcase how a BiI3 thin films can be converted into (CH3NH3)2Bi2I9 perovskite by means of exposure to MAI vapour.2 Furthermore, the conversion of BiI3 mesoporous films to MBI perovskite is monitored using the controlled vapors-assisted solution process (VASP) was investigated in detail, using films of BiI3 and MBI on mesoporous TiO2. The strong exciton absorption and improved crystallinity and homogeneous surface coverage was monitored by XRD and surface morphology SEM images respectively. The stoichiometric elemental analysis using HAXPES shows formation of MBI phase during the entirety of the timed-growth synthesis. Furthermore, HAXPES shows the presence of (metallic) Bi0. The metal content is substantially reduced after longer vapors-assisted growth (25 and 45 min BiI3 + MAI vapors, mitigating metal defect sites and im- proving semiconducting properties that resulted in improved photo- voltaic efficiency. The variation in the electronic structure in the series is only related to Fermi level of the samples, affecting charge-transfer of photo-excited carriers that are favorable in a mesoporous TiO2 scaffold. Solar cells made from BiI3 and MBI (different reaction time between precursor BiI3 + MAI vapors) sample showed improved performance with efficiency of 0.34% for mesoporous Bismuth triiodide and because of improvement in crystallinity and surface morphology on reaction of BiI3 with MAI vapors record highest efficiencies of 3.17–1.87% obtained2 Perovskite solar cell technology facing major challenges relating to developing non-toxic, largescale production scheme. In continuation to above work and in direction to produce all non-toxic solar cell, the talk will demonstrate fabrication of a lead-free perovskite solar cell without the use of toxic solvents. The high quality of the films was confirmed from X-ray diffraction, optoelectronic and X-ray photoelectron spectroscopy characterization. The devices fabricated with Spiro-OMeTAD and P3HT as the HTL yielded 1.12% and 1.62% efficiency. In addition, a more stable back contacts replacing the unstable silver and expensive gold metal electrodes is employed that adds the additional advantage of improved scalability and lowering of the material costs. This study, using an ‘all green' approach using a non-toxic solvent and avoiding the use of lead, while yielding crystal qualities and efficiencies on par with previous routes using toxic solvents, may aid scaling up lead and toxic solvent-free technology and thus facilitating its widespread utilization. In the end the talk will present a doping approach to improve the optoelectronic characteristics of MBI films – that recently resulted into efficiency over 6% for MBI based perovskite solar cells.4 Keywords: Bismuth, (CH3NH3)2Bi2I9, Lead-free perovskite solar cells, Non-toxic perovskite solar cells

Authors : Amal Bouich 1,Shafi Ullah 1, Julia Mari 1, ,Alexander Stewart 1,Asmaa bouich 2, Bernabé Mari 1, Mohamed Ebn Touhami 2
Affiliations : 1-Institute of Design & Fabrication (IDF) – Polytechnic University of Valencia UPV, Spain 2-Laboratoiry (LMEE)- Ibn Tofail university of Kenitra, Morocco

Resume : Herein, we investigate the effect of the organic/inorganic cation on the structural, morphological properties and stability of solution processed lead iodide perovskite thin films APbI3 (where A=MA, FA, Cs) prepared by one step spin coating technique in order to better understand their properties and optimize their chemical composition to meet the requirement of different applications. The influence of the different the organic/inorganic cation in the APbI3 films was investigated. The crystal structures, surface morphology and optical properties have been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), Transmission electron microscopy (TEM), photoluminescence and UV–Visible spectrometer, respectively. The crystalline structure of perovskite was found in the orientation of (110) plane. It is observed from the XRD results that the type of the cation plays an important role in in growth and stabilization of the APbI3. Here, the cesium leads to smooth and homogenous surface and large grain size and pinhole-free perovskite film. The optical analysis revealed that the band gap is in the range from 1.4 to 1.8 eV for the different cations. Furthermore, in a ~60% humid environment and after two weeks the stability of CsPbI3 was found that remain excellent. Key words: Thin films, Hybrid perovskite, Photoluminescence, compositional engineering, phase stability.

Authors : Shyantan Dasguptaⴕ1,4, Taimoor Ahmadⴕ2,3, Samy Almosni2, Senol Oez2, Konrad Wojciechowski1,2 ⴕBoth authors have equal contribution
Affiliations : 1: Saule Research Institute; Dunska11, Wroclaw 54-427, Poland 2: Saule Technologies Ltd.; Dunska11, Wroclaw 54-427, Poland 3: University of Rome “Tor Vergata”, Department of Electronics Engineering, Via del Politecnico 1, 00133 Rome, Italy 4: Faculty of Materials Engineering and Technical Physics, Poznan University of Technology, Piotrowo 3, Poznan 60-965, Poland

Resume : AN ENCAPSULATION STUDY FOR FLEXIBLE PEROVSKITE SOLAR CELLS TO WITHSTAND HIGH TEMPERATURE AND HUMIDITY CONDITIONS Shyantan Dasguptaⴕ1, Taimoor Ahmadⴕ2, Konrad Wojciechowski1,2 1: Saule Research Institute; Dunska11, Wroclaw 54-427, Poland 2: Saule Technologies; Dunska11, Wroclaw 54-427, Poland ⴕ Both authors contributed equally ABSTRACT: Perovskite solar cells attracted a lot of interest in the photovoltaic community in the recent years, recording a very fast pace of improving photovoltaic performance. Versatile and low temperature fabrication methods of functional layers in these devices enable application of flexible, polymeric substrates. This, in turn, opens the possibility of offering new, disrupting solutions, such as low-cost manufacturing (roll-to-roll processing), mechanical flexibility, and high specific power. However, the long-term reliability of these devices poses one of the major concerns for the large-scale utilization of the perovskite technology. Recently, multiple reports showed significant progress in reported stabilities of perovskite solar cells when subjected to accelerated aging tests, including conditioning at elevated temperature (85 oC). In order to pass damp heat test (85 oC, 85% RH), one of the most demanding tests in IEC reliability norms, robust device encapsulation needs to be realized, which is still a challenge for flexible architectures. In this work, we have tested various encapsulation structures (different adhesives, barrier materials, edge sealants, busbar connections) of perovskite devices with a carbon back contact electrode and subjected them to 85 oC aging tests in inert (glovebox) or high humidity (climate chamber, 85% RH) conditions. We have obtained effective laminates, showing promising stability in the aging test, indicating robust encapsulation. Furthermore, we have identified significant impact of various processing steps (edge sealing, busbar connection, lamination pressure, etc.) on reliability result.

Authors : Gabriel J. Man, Pabitra K. Nayak, Håkan Rensmo, Sergei M. Butorin
Affiliations : Uppsala University; Tata Institute of Fundamental Research; Uppsala University; Uppsala University

Resume : Lead halide perovskite (HaP) materials of the form ABX3 have attracted substantial global research interest for over a decade and commercial solar cell and light-emitting diode (LED) applications are starting to appear on the market. The A-site cation (A-cation) can be an organic or inorganic cation (methylammonium, formamidinium, cesium), the B-site cation is lead in the most well studied HaPs, and the X-site cation can be iodide, bromide, chloride. In spite of the recent research interest and a history of basic research dating back to as early as the 1970's, there are fundamental questions to be answered. One concerns the optoelectronic function of the A-cation. Solar cell and mechanical nano-indentation studies suggest the A-cation does not play an optoelectronic role, while time-resolved photoluminescence studies suggest it does. In the Condensed Matter Physics of Energy Materials program of the Division of X-ray Photon Science at Uppsala University, we perform atomic-level investigations of energy materials via a variety of synchrotron-based and time-resolved X-ray-based spectroscopies. We have previously reported comparisons between Photoelectron Spectroscopy (PES) measurements on HaP thin films and density-of-states (DOS) calculations. However, the optoelectronic role of the A-cation remained unclear. We have now exploited the element-selectivity and site-specificity of core level spectroscopies and the higher sample quality offered by single crystals to provide new information that builds on past studies by others and us. Here we report our findings that are relevant for unraveling this scientific mystery, utilizing the first application of core level spectroscopy to single crystals of HaPs. I will present a comparative study of three archetypal lead bromide perovskite (APbBr3) compounds using Br K-edge high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS) and simulated XAS spectra. We find a nearly linear correlation between relative Goldschmidt tolerance factor, a widely used structural descriptor that is affected by the size of the A-site cation, and the energetic width of the conduction band. These findings are potentially relevant for understanding the mechanism of slow hot electron cooling in HaPs. Using Br K non-resonant X-ray emission spectroscopy (NXES), we find relative differences in lead-bromide bond ionicity. These results are potentially relevant for understanding the origin of A-cation-related trends in device-relevant energy levels, which are crucial for designing HaP device interfaces. Our studies challenge a notion based on previous studies that the A-cation is electronically inert.

Authors : Anurag Krishna1‡*, Hong Zhang2, Zhiwen Zhou2, Thibaut Gallet3, Mathias Dankl4, Olivier Ouellette2, Felix T. Eickemeyer2, Fan Fu6, Sandy Sanchez1, Mounir Mensi7, Shaik M. Zakeeruddin2, Ursula Rothlisberger4, G. N. Manjunatha Reddy5, Alex Redinger3, Michael Grätzel2, Anders Hagfeldt1*
Affiliations : 1Laboratory of Photomolecular Science, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland. 2Laboratory of Photonics and Interfaces, École Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland. 3Scanning Probe Microscopy Laboratory, Department of Physics and Materials Science, University of Luxembourg, Luxembourg. 4Laboratory of Computational Chemistry and Biochemistry, École Polytechnique Fédérale de Lausanne, Lausanne 1015, Switzerland. 5Univ. Lille, CNRS, Centrale Lille Institut, Univ. Artois, UMR 8181-UCCS-Unité de Catalyse et Chimie du Solide, F-59000 Lille, France 6Laboratory for Thin Films and Photovoltaics, Empa-Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland. 7Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Valais Wallis, CH-1951 Sion, Switzerland. ‡ Presenter: Email: (A.K.) *corresponding author (e-mail): (A.K.), (A.H.)

Resume : Perovskites are among the most promising photovoltaic materials with power conversion efficiencies (PCEs) exceeding 25%. However, long-term operational stability remains the primary concern for perovskite solar cells (PSCs). Consequently, there is a quest for searching for new compositions and interface materials that enable stable-efficient PSCs. Herein, we report a facile molecular-level interface engineering strategy based on multifunctional molecules for interface passivation to reduce defects, passivate grain boundaries, and suppress the ion migration across the interface. We have combined the functionalities associated with different anchoring groups into a single molecule, which in turn can bind to the perovskite crystal through non-covalent interactions. The interface engineered solar cells exhibited high operational stability (maximum powering point tracking at 1 sun illumination) with a stabilized T80 (the time over which the device efficiency reduces to 80% of its initial value) of ≈5950 h at 40 ºC and stabilized efficiency over 23%. The origin of high device stability and performance is correlated to the nano/sub-nanoscale molecular level interactions between ligand and perovskite layer, which is corroborated by comprehensive multiscale characterizations. Our results provide key insights into the modulation of the grain boundaries, local density of states, surface bandgap, and interfacial recombination. Chemical analysis of the aged devices showed that molecular passivation inhibited interfacial ion migration and prevented photoinduced I2 release that irreversibly degrades the perovskite. This study shows that tailoring the interface is the key to overcome stability issues associated with the high-performing hybrid perovskite compositions, thus allowing a step closer to achieving the long-standing stability of perovskite-based solar cells.

Authors : Davide Raffaele Ceratti, Philip Schulz, et Jean Francois Guillemoles
Affiliations : Institut Photovoltaïque d'Ile-de-France (IPVF) / 18 Boulevard Thomas Gobert, 91120 Palaiseau; Institut Photovoltaïque d'Ile-de-France (IPVF) / 18 Boulevard Thomas Gobert, 91120 Palaiseau; Institut Photovoltaïque d'Ile-de-France (IPVF) / 18 Boulevard Thomas Gobert, 91120 Palaiseau;

Resume : The widely used Methylammonium (MA ) and Formamidinium (FA ) cations are relatively acidic compounds, with the potential to dissociate in the halide perovskites, giving a proton (H ) and the corresponding ammine. Despite the fact that they were considered not to do so, I will bring new evidence that the dissociation does happen and that H can migrate, associate with eventual water molecules internalized in the perovskite, be absorbed by basic hole transporting layers and other related phenomena. I will also comment on the chemistry of H in solution and show how it influences the final state of a perovskite layer after the coating. As it happens in general, in the perovskites the chemistry of protons is reversible and is characterized by chemical equilibria, which are modified by a large number of factors. I will provide indications on how temperature, illumination intensity, electronic doping of the perovskite material and the presence of other molecules pushes the acid-base equilibrium towards the dissociation or the association. The complexity of these equilibria is at the base of a series of phenomena that have been observed in halide perovskites like fast ion-migration, light-soaking and reversible damage repair (self-healing). In this talk, I will provide proof of the migration of protons in the perovskites as obtained by exchange of H with deutons (D ) and discuss their diffusion coefficient in halide perovskite single crystals. Through optical microscopy (confocal, hyperspectral, fluorescence lifetime imaging spectroscopy), I will also provide proof on how the proton chemistry influences the photoluminescence of the perovskites showing how proton deficient perovskites have better optoelectronic properties. In particular, I will analyze how the positive effects of methylamine treatment in the perovskites can be related to proton chemistry and how light might locally originate methylamine causing the effect of light soaking in the perovskites. I will also show that H acts as an oxidizer when the perovskite is put into contact with metals and its influence should be considered when depositing contacts directly on the perovskite material. I will also analyze the chemistry of protons in the perovskite precursor solutions showing how their presence influences which particular lead complexes are actually in solution during crystallization. I will show how the electrochemical potential of the precursor solution (and therefore of the perovskite material) is partially determined by the presence of protons with consequences on the quality and quantity of defects in the perovskite materials. To conclude, the aim of this talk is to provide the listener a wide view on proton chemistry in halide perovskites providing the theoretical tools to understand the influences that proton chemistry has on the optoelectronic properties and the stability of the perovskites. This talk will be rich in chemical knowledge but it will be adapted to an audience working on halide perovskite devices with more engineering or physics background.

15:45 Q&A live session / Break    
A-4 : Pritam Panda, Uppsala University
Authors : Hrubiak A.B.(1), Moklyak V.V.(1), Gogitidze Z.D.(2)
Affiliations : (1) G.V.Kurdyumov Institute for Metal Physics, N.A.S. of Ukraine, Ukraine; (2) Medical Information Center "Regul Medical", Ukraine

Resume : In the work we shows a new approach to improving the performance of lithium power sources by using the polypeptides and composites based on them as an active component of the cathode composition. Standard tests of the "Biopolimer Lithium Power Sourses " in galvanostatic mode were carried out in laboratory prototypes of the Swagelok type CR2032 format in the potential range from 1.0 to 4.0 V relative to Li/Li+ with current densities of 10÷100 mA/g. The experimental profiles of the discharge curves has a classic S-shape with the formation of a potential plateau in the range of 2.5-1.8 V depending on the relative volume of polypeptides in the cathode composition. The optimal result has been established in terms of reaching the maximum specific capacity of 2750 mAh/g (in terms of the mass of active organic components) and the values of the discharge potentials plateau 2.1-1.8 V for prototypes with current densities of 10 mA/g. The obtained values of the specific discharge capacity significantly exceed those of all available types of cathodes, both theoretical and experimental. Subsequently, we functionalized the surface of thermally expanded graphite by low molecular weight polypeptides by depositing them on the reaction surface and used such composites as the active base of the cathode for lithium power sources. In this case, the functionalization of the surface implies a multiple increase in the trapping centers of lithium ions during the course of electrochemical reactions due to the attraction of various radicals of the polypeptide chain attached to the carbon surface to the current-forming process. The obtained experimental discharge curves demonstrate the specific discharge capacity at the level of 19000 mAh/g for a current density of 10 mA/g, which is almost an order of magnitude higher than similar discharge indices what we received earlier. An increase in the discharge current density to 20 mA/g leads to decrease in the specific discharge capacity to 7900 mAh/g. A further increase in the discharge current density causes a decrease in the value of the specific discharge capacity according to the exponential law with saturation reaching 1500 mAh/g at a current density of 100 mA/g. So, the "Biopolimer Lithium Power Sourses" with a biopolymer-based cathode opens a new concept of ultra-high capacity of lithium power sourses. The mechanisms of stream-forming processes in such a battery are associated with stability of polypeptides and biocompatibility of inorganic components with them, what during the discharge process makes possibility to implement a number of mechanisms of electrochemical transformations with the participation of a highly developed lateral surface of the biopolymer chain through electrochemical reactions and surface adsorption/desorption of cations.

Authors : Lucia N. Leonat 1, Viorica Stancu 1, Andrei Tomulescu 1,2 , Ioana Pintilie 1
Affiliations : 1 National Institute of Materials Physics, Atomistilor 405A, 077125, Magurele, Ilfov, ROMANIA 2 University of Bucharest, Faculty of Physics, Atomistilor 405A, 077125, Magurele, Ilfov, ROMANIA

Resume : Perovskite solar cells have reached the maximum efficiency due to the consistent optimization of each component layer. However, at laboratory scale they are fabricated using the usual spin-coating method in a controlled atmosphere without moisture and oxygen. For commercial purposes, solar cells with large active areas are required. Therefore, the spin coating method is no longer suitable for manufacturing solar cells with an area larger than 1 cm2. Moreover, large area solar cells are made in inverted geometry, because it is easier to obtain polymeric charge selective thin films with alternative large-area deposition methods, such as slot-die, doctor blade, etc. In this work, we fabricated large-area solar cells, with an active area of 2.4 cm2, in a standard geometry, FTO/ TiO2 compact&mesoporous/ Perovskite/ Spiro O Me-TAD/ Au, using alternative fabrication methods. We used the spray deposition method for fabricating the compact and mesoporous TiO2 layers in ambient atmosphere [1] and a blade-coating technique in ambient environment for the perovskite film deposition and for the p-type layer, spiro O Me-TAD. Spray coating of the mesoporous suspension leads to the formation of a characteristic “reticulated structure” with a high roughness, which is in fact beneficial for the charge separation at the interface with the perovskite layer. For the proper perovskite crystallization, we used a precise control of the substrate during deposition, and added DMSO to the precursor solution to delay crystallization. The as-prepared perovskite films presented large crystalline domains and good settling to the rough mesoporous scaffold. [1 ]. Tomulescu, A. G.; Stancu, V.; Beşleagă, C.; Enculescu, M.; Nemneş, G. A.; Florea, M.; Dumitru, V.; Pintilie, L.; Pintilie, I.; Leonat, L. “Reticulated Mesoporous TiO2 Scaffold, Fabricated by Spray Coating, for Large‐Area Perovskite Solar Cells”, Energy Technology 2019, 1900922.

Authors : Qingqing Wang*, Xianjie Liu & Mats Fahlman
Affiliations : Department of Science and Technology, Linköping University, Sweden

Resume : Two-dimensional molecular crystals[1,2] (2DMCs) featuring a monolayer (ML) or few layers of molecules, are attracting intensive research attention due to the advantages of long-range molecular ordering, minimized concentration of charge traps, the absence of grain boundaries, and so on, providing an exciting prospect for (opto)electronic applications. For applicative purpose, the improvement of electronic conductivity of 2DMCs can be achieved by n-type doping. The doped 2DMCs not only provide the information about doped 2DMCs itself, but also physical phenomena which are associated with charge-carrier transport at interface. To date, most theoretical and experimental investigations focus on alkali-doped organic polymer [3] and fullerene film [4]. There are only very few investigations on the nature of alkali-doped into 2DMCs assembled via weak van der Waals. Here, we study the electronic structure of potassium-doped 2DMCs of C6-DPA as a function of potassium incorporation by ultraviolet photoelectron spectroscopy (UPS) and X-Ray photoelectron spectroscopy (XPS). When doped by potassium, we observed that (i) C6-DPA electronic states shifts to high binding energy as the potassium concentration increases, (ii) at low doping level, singly-charged polarons formed in the energy gap firstly, followed by polaron-to-bipolaron transition as doping increased, (iii) dispersion occurs for the potassium-induced bipolaron, (Ⅳ) the transformation of peak corresponding to the delocalized Π-orbital. our experiments provide evidence for the impact of potassium doping on the 2DMCs, which can be assigned to the change of 2DMCs structure and the formation of polaron-to-bipolaron transition, also guide us to evaluate the energy-level alignment at the 2DMCs/substate interface, and thus to construct high-performance device. [1] Yang F. X., Hu W. P., Adv. Mater. 2018, 30, 1702415 [2] Qian J., Li Y., Adv. Mater. Technol. 2019, 4, 1800182 [3] Chen G. H., Li H. N., ACS Omega 2019, 4, 8087−8093 [4] Wienk, M. M.; Janssen, R. A. J., Angew. Chem., Int. Ed. 2003, 42, 3371−3375.

Authors : Tim Freund Laura Manuel Peter Wellmann
Affiliations : Friedrich-Alexander Universität Erlangen-Nürnberg, Institute of Materials for Electronics and Energy Technology; Friedrich-Alexander Universität Erlangen-Nürnberg, Institute of Materials for Electronics and Energy Technology; Friedrich-Alexander Universität Erlangen-Nürnberg, Institute of Materials for Electronics and Energy Technology

Resume : While chalcogenide perovskites, like BaZrS3, are considered as emergent solar cell materials, [1] few synthesis routes have been established so far, with the most commonly ones being solid state synthesis [2, 3] and sulfurization of the respective oxide perovskite. [4, 5] Electrodeposition is a technique commonly used to deposit metals onto various substrate, and also has been established in the field of chalcogenide semiconductors such as Cu(In,Ga)Se2 (CIGS) and Cu(Zn,Sn)(S,Se)3 (CZTS). [6] The most prominent advantages of electrodeposition are low price, high-throughput compatibility and ease of fabrication. [7] Therefore, the synthesis of thin films based on chalcogenide perovskites should be explored. However, the immediate deposition of a ternary or quaternary compound generally is challenging as a multitude of constituents and parameters must be considered. Therefore, the deposition of ZrSe2 precursor thin films from aqueous solution was chosen as a gateway for this work, as this process is established in the literature. [8] From this point, a BaS layer can be deposited on top using electron beam deposition and the resulting stack subsequently annealed at elevated temperatures up to 1600°C to form the quaternary compound BaZr(S,Se)3. This approach can be taken even further by trying to incorporate barium ions into the system to directly deposit the ternary compound BaZrSe3. And even further, it should be attempted to replace the selenium source with a suitable sulphur containing compound should to potentially directly deposit BaZrS3 thin films, which is the most common chalcogenide perovskite synthesized by other groups. The results and progresses obtained following this pathway will be presented. 1. Sun, Y.Y., et al., Chalcogenide perovskites for photovoltaics. Nano Lett, 2015. 15(1): p. 581-5. 2. Hahn, H. and U. Mutschke, Untersuchungen über ternäre Chalkogenide. XI. Versuche zur Darstellung von Thioperowskiten. Zeitschrift für anorganische und allgemeine Chemie, 1957. 288(5‐6): p. 269-278. 3. Ravi, V.K., et al., Colloidal BaZrS3 Chalcogenide Perovskite Nanocrystals for Thin Film Device Fabrication. Nanoscale, 2021. 4. Gupta, T., et al., An Environmentally Stable and Lead-Free Chalcogenide Perovskite. Advanced Functional Materials, 2020. 30(23): p. 2001387. 5. Shaili, H., et al., Synthesis of the Sn-based CaSnS3 chalcogenide perovskite thin film as a highly stable photoabsorber for optoelectronic applications. Journal of Alloys and Compounds, 2021. 851. 6. Chandran, R., S.K. Panda, and A. Mallik, A short review on the advancements in electroplating of CuInGaSe2 thin films. Materials for Renewable and Sustainable Energy, 2018. 7(2). 7. Pandey, R.K., Sahu, S. N., Chandra, S. , Handbook of Semiconductor Electrodeposition. Applied Physics, ed. A.M. Herrmann. 1996, New York: Taylor & Francis. 8. Rakkini, A.P.V. and K. Mohanraj, Effect of different combinations of precursors of zirconium and selenium in the electrodeposited ZrSe2 thin films. Ionics, 2018. 24(4): p. 1243-1252.

Authors : M. Anglada, E. Ros, D. Rovira, C. Voz, P. Ortega, J. Bertomeu, J. López, J.M. Asensi, M. Guc, V. Izquierdo, E. Saucedo, J. Puigdollers, J. Llorca
Affiliations : M. Anglada, J. Llorca. Dept Eng Química, UPC; J. Bertomeu, J. López, J.M. Asensi. Dept Física Aplicada, UB; M. Guc, V. Izquierdo. Dept Solar Energy Materials, IREC; E. Ros, D. Rovira, C. Voz, P. Ortega, E. Saucedo, J. Puigdollers. Dept Eng Electrònica, UPC;

Resume : Ultrathin dielectric layers of amorphous TiOx and AlOx were deposited on top of sol-gel prepared anatase titania samples and tested for the hydrogen evolution reaction from water-ethanol mixtures. TiOx and AlOx films were deposited by atomic layer deposition (ALD) at a deposition temperature of 100 ºC, with H2O + Trakis(dimethylamido)titanium(IV) as precursor for TiOx and H2O + Trimethylaluminium for AlOx. Various thicknesses of both dielectrics were tested, ranging from 0.4 to 2 nm for TiOx and 0.4 to 1 nm for AlOx. Enhancement of the photocatalytic activity was found for thicknesses below 1.2 nm of titania with the 0.4 nm thickness layer being the one with the highest photocatalytic activity, doubling that of the non-passivated sample. For TiO2 layers thicker than 1.2 nm photocatalytic activity decreased drastically, being almost null for a 2 nm layer. On the other hand, for alumina passivating layers, the only thickness that improved the results of the non-passivated sample was 0.4 nm, with thicker layers decreasing the photocatalytic activity. The passivation effect was also analysed by photothermal deflection spectroscopy (PDS) to see the reduction of defect mid-gap states, and high resolution transmission electron microscopy (HRTEM) to observe the nanostructure of the materials. Moreover, samples were analyzed by means of Raman and photoluminescence (PL) spectroscopies. Measurements were performed in backscattering configuration using the 325 nm excitation wavelength at room temperature. Raman spectroscopy shows presence of main anatase TiO2 phase with insignificant variations in the spectra of the samples exposed to passivation. PL spectrum of the reference sample shows a broad band with the maximum close to 2.5 eV related to the TiO2 emission. Analysis of the PL spectra exhibited a pronounced decrease of the relative quantum yield of the radiative emission while passivating the amatase layer with TiOx layer. On the other hand, this effect is less pronounced or is not present in the anatase layer passivated by different thickness of AlOx layer. Our findings indicate a reduction of the recombination centres because of the effect of passivating layers, especially with TiOx, highly improving the rates of hydrogen production. Differences between TiOx and AlOx performance can be explained by the difference in ethanol adsorption enthalpy on their surface. Finally, the nature of the changes in PL spectra and influence of the thickness of different passivation layers to the radiative properties of the nanoparticles will be discussed during the presentation.

Authors : Marina I. Ustinova [1]*, Maria M. Mikheeva [2,3], Gennady V. Shilov [1], Nadezhda N. Dremova [1], Lyubov Frolova [1], Sergey M. Aldoshin [1], Keith J. Stevenson [2], and Pavel A. Troshin [1]
Affiliations : 1 Institute for Problems of Chemical Physics of Russian Academy of Sciences (IPCP RAS) 2 Skolkovo Institute of Science and Technology 3 D. Mendeleev University of Chemical Technology of Russia (MUCTR)

Resume : All-inorganic lead halide perovskites, e.g. CsPbI3, are becoming more attractive for applications as the light absorbers in perovskite solar cells due to a higher thermal and photochemical stability as compared to their hybrid analogs. However, the specific drawback of CsPbI3 absorber consists in the rapid phase transition from black to yellow non-photoactive phase at low temperatures (e.g. <100 oC), which is accelerated under exposure to light. Herein, an experimental screening of an unprecedently large series (>30) of metal cations in a wide range of concentrations has allowed us to establish a set of Pb2+ substitutes facilitating the crystallization of the photoactive black CsPbI3 phase at low temperatures. Importantly, the appropriate Pb2+ substitution with Ca2+, Sr2+, Ce3+, Nd3+, Gd3+, Tb3+, Dy2+, Er3+, Yb2+, Lu3+, and Pt2+ cations has led to a spectacular enhancement of the film stability under realistic solar cell operation conditions (~1 sun equivalent light exposure, 50 oC). Optoelectronic, structural, and morphological effects of partial Pb2+ substitution were investigated providing a deeper insight into the processes underlying the stabilization of CsPbI3 films. Several CsPb1-xMxI~3 systems were evaluated as the absorber materials in perovskite solar cells demonstrating encouraging light power conversion efficiency of 11.4% in preliminary experiments. The obtained results feature the potential of designing efficient and stable all-inorganic perovskite solar cells using novel absorber materials rationally designed via the B-site engineering. More details can be found in our paper: M.I. Ustinova et al., Partial Substitution of Pb2+ in CsPbI3 as an Efficient Strategy to Design Fairly Stable All-Inorganic Perovskite Formulations. ACS Appl. Mater. Interfaces, 2021, 13(4):5184-5194.

Authors : Ursi F.(1), Ferrario A.(2), Boldrini S.(2), Giannici F.(1), Pipitone C.(1), Martorana A.(1)
Affiliations : (1) Dipartimento di Fisica e Chimica, Università di Palermo, viale delle Scienze, I-90128, Palermo, Italy (2) CNR - ICMATE, Corso Stati Uniti 4, I-35127, Padova, Italy

Resume : Thermoelectric devices have been mostly based on inorganic compounds; yet, hybrid thermoelectric materials have recently attracted a great deal of attention for the development of wearable electronics, such as fitness trackers, smartwatches, and medical sensors, fed by the heat produced during metabolic processes. [1] This latter class of devices should join good TE efficiency and suitable fitting to the human body, as allowed by flexible TE materials. Hybrid TE materials, combining inorganic electrical conductivity with typically organic flexibility, good TE properties at low temperatures, and high thermal resistivity, are particularly suited for these applications. [2] In this paper, we present the physical-chemical characterization and the evaluation of thermoelectric properties of 2D transition metal dichalcogenide (TMD) - amine compounds obtained by a simple mechanical grinding process allowing the intercalation of ethylenediamine, hexylamine, heptylamine, and octylamine in the van der Waals gap of TiS2 and 2H-MoS2. 1. H. Jin, J. Li, J. Iocozzia, X. Zeng, P. C. Wei, C. Yang, N. Li, Z. Liu, J. H. He, T. Zhu, T. Zhu, J. Wang, Z. Lin, S. Wang, Hybrid Organic-Inorganic Thermoelectric Materials and Devices, Angew. Chem. Int. Ed. 58 (2019) 15206 – 15226. 2. S. Ferhat, C. Domain, J. Vidal, D. Noël, B. Ratier, B. Lucas, Flexible thermoelectric device based on TiS2(HA)x n-type nanocomposite printed on paper, Organic Electronics 68 (2019) 256-263.

Authors : Victoria. V. Ozerova [1,2], Lyubov A. Frolova [2], Nikita A. Emelianov [2], Sergey M. Aldoshin [2], Pavel A. Troshin [2]
Affiliations : 1. Mendeleev University of Chemical Technology, Moscow, Russia; 2. Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia

Resume : Low operational stability of perovskite solar cells represents a bottleneck issue hampering the commercialization of this exciting photovoltaic technology. Among different approaches proposed to tackle this problem, a particular promising is the application of so-called passivation coatings for modification of perovskite films. Typically, these are very thin (sometimes even monomolecular layers) films of some reagents that are introduced atop the absorber films or at the grain boundaries to decrease the density of defects and improve photovoltaic performance and/or operational stability of perovskite solar cells. There are hundreds of various additives or passivation coatings tested directly in photovoltaic cells, whereas the information on their action mechanisms is very scarce and controversial. One of the reasons is that these passivation coatings were mostly screened towards improving the ambient stability of perovskite solar cells, which is probably not the best approach since efficient encapsulation should solve the extrinsic stability problem. Surprisingly, there are almost no studies on the effect of such passivation coatings on the intrinsic photochemical and thermal stability of perovskite films. Obviously, having no such fundamental information it is hardly possible to draw any reliable conclusions about action mechanisms of certain passivation coatings or processing additives. Herein, we performed a systematic study to fill the aforementioned gap in knowledge. In particular, we investigated the impact of a broad range of passivation reagents (>30 compounds) on the intrinsic photochemical and thermal stability of perovskite thin films under well-controlled anoxic conditions. The influence of such parameters as loading of passivation additives in the perovskite ink, processing of passivation coatings above the absorber films, and their thickness were studied. The obtained results allowed us to (1) identify the most promising passivation coatings, (2) elaborate the appropriate procedures for passivation of perovskite films, (3) establish correlations between the molecular structures of the additives and their stabilization effect induced in perovskite films and (4) draw some conclusions about the action mechanisms of the most promising passivation coatings. The performed studies featured a tremendous potential of rationally designed passivation coatings to be used for blocking main intrinsic degradation pathways in complex lead halides and boosting spectacularly the operational stability of perovskite solar cells.

Authors : Alba Díaz-Lobo1, Ángel Morales Sabio2, Marisol Martín-González1, Cristina V. Manzano1
Affiliations : 1. Instituto de Micro y Nanotecnología (IMN-CNM), CSIC (CEI UAM+CSIC), Isaac Newton 8, E-28760, Tres Cantos, Madrid, Spain; 2. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Avda. Complutense 22, E-28040, Madrid, Spain;

Resume : Passive radiative cooler technology enables buildings and surfaces all-day-cooling without power input. In order to achieve an efficient performance of the cooler, two characteristics have to be accomplished: high reflectance in the solar spectrum range as well as high emissivity in the atmospheric window wavelengths. Several attempts with different nanostructures have been studied. In particular, anodic aluminium oxide (AAO) nanostructures have been recently presented as a promising material, due to both its tunable photonics properties and its low-cost. A global analysis of the nanopores AAO membranes is shown in this work. Different electrolytes, such as sulfuric acid, sulfuric acid with ethylene glycol, oxalic acid, and phosphoric acid have been considered in a two-step anodization fabrication process [1-5]. The anodization conditions and the chemical post-treatment are varied to modify the morphology of the membranes: pore diameter, interpore distance, porosity, order grade, and thickness. Finally, the optical response has been characterised in the ultraviolet, visible, and infrared ranges for the different morphologies to find the most accurate one to passive radiative cooler applications. References: 1. Manzano, C., et al., The influence of thickness, interpore distance and compositional structure on the optical properties of self-ordered anodic aluminum oxide films. Journal of Materials Chemistry C, 2016. 4(32): p. 7658-7666. 2. Manzano, C.V., et al., Controlling the color and effective refractive index of metal-anodic aluminum oxide (AAO)–Al nanostructures: Morphology of AAO. The Journal of Physical Chemistry C, 2018. 122(1): p. 957-963. 3. Manzano, C.V., J. Martín, and M.S. Martín-González, Ultra-narrow 12 nm pore diameter self-ordered anodic alumina templates. Microporous and Mesoporous Materials, 2014. 184: p. 177-183. 4. Martín, J., et al., High-aspect-ratio and highly ordered 15-nm porous alumina templates. ACS applied materials & interfaces, 2013. 5(1): p. 72-79. 5. Martín, J., C.V. Manzano, and M. Martín-González, In-depth study of self-ordered porous alumina in the 140–400 nm pore diameter range. Microporous and Mesoporous Materials, 2012. 151: p. 311-316.

Authors : Egidijus Kamarauskas, Romualdas Jonas Čepas, Vygintas Jankauskas, Kristijonas Genevičius
Affiliations : Vilnius University, Faculty of Physics, Institute of Chemical Physics

Resume : Organic materials gain a lot of attention as promising new materials for solar cells, field effect transistors, detectors, due their simple deposition techniques and cheap synthesis. Although organic materials suffer from instability under ambient conditions, various techniques are used to improve chemical stability, mechanical strength. One of the promising methods is cross linking, which improves mechanical properties, but usually it has negative impact on electrical properties, such as charge carrier mobility. In order to better understand the influence of cross linking on charge transport, we have investigated a few novel compounds with cross linking ability using various methods, such as time-of-light (TOF) and extraction of the charge carriers by linearly increasing voltage (CELIV). Herein we present, how cross linking affects on charge carrier mobilities, recombination losses, disorder in crosslinked and non-crosslinked thin films made from investigated compounds.

Authors : M. García-Carrión1, R. Martínez-Casado1, J. Ramírez-Castellanos2, E. Nogales1, and B. Méndez1
Affiliations : 1.Department of Physics of Materials, Faculty of Physical Sciences, University Complutense Madrid, 28040, Madrid, Spain; 2.Department of Inorganic Chemistry, Faculty of Chemical Sciences, University Complutense Madrid, 28040, Madrid, Spain

Resume : Nanocomposites formed by oxide nanoparticles embedded in conducting polymers have recently been proposed as excellent candidates to be used as top electrodes in hybrid solar cells, due to the expected improvement on the electrical properties. In particular, composites of PEDOT:PSS polymer with Ga2O3 nanoparticles (beta- and gamma phases) as additive have been tested as coating layers on Si wafers and higher minority carrier lifetimes were achieved in comparison with the reference polymer [1]. However, the underlying physical properties of the Ga2O3 nanoparticles have not been fully assessed. In this work, the electronic levels of the monoclinic (beta-) and cubic (gamma-) phases of Ga2O3 have been explored by means of non-invasive and contact-less luminescence techniques, which collect radiative recombination energy levels from electronic states in the material. These nanoparticles have been synthesized by a chemical route followed by a thermal treatment at 250ºC or 750 ºC to produce the gamma- or the monoclinic phase, respectively. The luminescence properties have been assessed by cathodoluminescence (CL) in the scanning electron microscope (SEM) and by photoluminescence (PL). Beta-Ga2O3 nanoparticles showed both ultraviolet and blue emissions in CL and selective PL spectra, while gamma-phase nanoparticles led to a dominant blue emission. In addition, a temperature dependent study of the PL has been performed in order to evaluate the activation energies of the non-radiative channels in both structures. The results will help to understand both optical and electrical properties of Ga2O3 nanoparticles, extending the knowledge of this material to the nanoscale and to its further implementation in energy devices. References [1] M. García-Carrión et al. Materials Letters, 261 (2020) 127088.

Authors : Paulina Kamińska, Piotr Śpiewak
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland

Resume : Nowadays, commercially used thermoelectric materials are based on Pb-Te or Bi-Te compounds, which are toxic and expensive. Therefore, it is crucial to find new materials for thermoelectric applications. Lately, materials based on sulfur, as one of the cheapest and most common elements, draw scientists’ attention due to promising performance. A few years ago, Terasaki reported that the oxide spinels such as NaxCoO2 and Ca3Co4O9 exhibit extraordinary TE performance. This phenomenon was explained by the different spin states of Co, which increase the Seebeck coefficient. Lately, Khan et al. have reported the thermoelectric properties of another spinel – CuCr2-xSbxS4. Although the pure CuCr2S4 is reported to be metallic, a minor addition of antimony makes the material semiconductive. They discovered a significant Seebeck coefficient exceeding 200 μV/K for doped CuCr2S4, compared to 16 μV/K for the pure material. Furthermore, they were able to achieve a maximum ZT ≈ 0.43 at 650ºC without the nanostructuring. This is one of the highest values reported for sulfur-based thermoelectric materials. The electronic transport parameters were also measured by the Hall effect, and the high carrier concentration of 2.41×1021 cm-3 at 300 K was revealed. In this work, density functional theory (DFT) calculations are employed to investigate the electronic properties of Fe, Co, Ni-doped thiospinel CuCr2S4. Transport properties are provided using Boltzmann’s transport theory. The DFT calculations are based on the semilocal general gradient approximation (GGA) in Perdew-Burke-Ernzerhof (PBE) parametrization for the exchange-correlation potential with Dudarev’s approach. It is found that the accurate description of the electronic band structure of CuCr2S4 requires the incorporation of spin-orbit coupling (SOC) in calculations. We show that ab initio calculations of doped CuCr2S4 can help find dopants other than antimony, changing the nature of studied spinel. Determining such dopants opens the way to finding materials with increased thermoelectric properties.

Authors : Stefan Andrei Irimiciuc1, Gabriela Dorcioman1, Petronela Garoi1, Doina Craciun1, Valentin Craciun1,2
Affiliations : 1National Institute for Laser, Plasma and Radiation Physics – NILPRP, 409 Atomistilor Street, Bucharest, Romania; 2Extreme Light Infrastructure for Nuclear Physics, Magurele, Romania

Resume : Low-density materials are of great interest for a wide range of applications. Recently, with the development of extreme high-power fs laser, they have been at the core of a series of experiments with strong impact for fundamental physics. In general, carbonaceous foams show exceptional properties: black-body-like absorption, an anomalous ferromagnetic behavior, increased gas and liquid adsorption and storage capability. The absorption of intense and short laser pulses by matter is observed to significantly increase in such density range. The advantage of using PLD for the deposition of such complex structure comes from inner properties of transient plasmas, which present strong density and temperature gradients, particle kinetic energy and in the case of carbon the presence of complex molecular structures forming at the front edge of the plasma. We report here on the generation of complex carbonaceous structures generated on silicon substrates by pulsed laser deposition of graphite target in controlled environment. A novel deposition geometry is implemented in order to take into account the flip-over effect and the strong asymmetries from the carbon generated plasma. The deposition process was calibrated by adjusting the laser beam energy, frequency, and deposition time on a wide range of values. Various background gasses (He, Ar, CH4) and pressure were used in order to find the best media that could aid the generation of complex carbon structures. The obtained films were investigated by complimentary surface analysis methods like XRD, XRR, XPS, SEM and EDS in order to accurately describe the structure and composition of the films. Acknowledgments: this work was supported by Romanian Ministry of Education and Research, under Romanian National Nucleu Program LAPLAS VI –contract n. 16N/2019, ELI-RO_2020_12 and Postdoctoral Project PD 145 ⁄ 2020

Authors : Annika Dehning; Birte Kressdorf; Jörg Hoffmann; Sarah Hoffmann-Urlaub; Stephan Melles; Christoph Flathmann; Michael Seibt; Christian Jooss
Affiliations : Institute of Materials Physics; Institute of Materials Physics; Institute of Materials Physics; Institute of Materials Physics; Institute of Materials Physics; IV. Physical Institute, IV. Physical Institute; Institute of Materials Physics, University of Göttingen, Germany

Resume : Strongly correlated manganites with their exceptional electric and magnetic properties are receiving a growing interest within the renewable energy community, e.g., for various application possibilities in electrochemistry and photovoltaic. Notably layered Ruddlesden-Popper Pr(0.5)Ca(1.5)MnO(4) (RP-PCMO) perovskite thin films constitute a key step towards hot polaron photovoltaics through a room-temperature charge- and orbital-ordered state [1]. This enables the investigation of new mechanism for photovoltaic energy conversion, overcoming conventional solar cells limitations of transmission and thermalization losses, by utilizing the phonon-electron interactions [1]. For this purpose highly crystalline films with a well-controlled growth on single-crystalline substrates are required. In this contribution we compare the growth mechanism of RP-PCMO on single crystal strontium titanate (STO) and titanium dioxide (TiO2) substrates with various crystal orientations. Although the lattice mismatch to RP-PCMO is rather large, theses substrates are of practical interest due to their doping facilities, e.g., Nb-doped STO or TiO2 can serve as the electron-doped part of RP-based pn-junctions. RP-PCMO films are deposited by means of ion beam and pulsed laser deposition techniques to gain insides into effects of growth conditions. The samples are investigated with X-ray diffraction (2𝜃-scan and ϕ-scan), atomic force microscopy, scanning and transmission electron microscopy. Epitaxial growth is observed on STO(110), STO(100) [2] and TiO2(110), where the films display an in-plane alignment of the c-axis. Special attention is given to the interface and possible diffusion interactions. Moreover the growth on Niobium doped conductive substrates (n-type Nb:STO [1] and Nb:TiO2) is compared to the undoped substrates and electric and photovoltaic properties of the junctions are investigated. References: [1] Kressdorf, B., Meyer, T., Belenchuk, A., Shapoval, O., Ten Brink, M., Melles, S., Ross, U., Hoffmann, J., Moshnyaga, V., Seibt, M., Blöchl P. & Jooss, C. (2020). Room-Temperature Hot-Polaron Photovoltaics in the Charge-Ordered State of a Layered Perovskite Oxide Heterojunction. Physical Review Applied, 14(5), 054006. [2] Hoffmann‐Urlaub, S., Ross, U., Hoffmann, J., Belenchuk, A., Shapoval, O., Roddatis, V., Ma, Q., Kressdorf, B., Moshnyaga, V, & Jooss, C. (2021). Tailoring c‐Axis Orientation in Epitaxial Ruddlesden–Popper Pr0.5Ca1.5MnO4 Films. Advanced Materials Interfaces, 8(7), 2002049.

Authors : Gamze Atak, İlknur Bayrak Pehlivan, José Montero, Claes G. Granqvist, Gunnar A. Niklasson.
Affiliations : Gamze Atak1,2; İlknur Bayrak Pehlivan1; José Montero1; Claes G. Granqvist1; Gunnar A. Niklasson. 1Department of Materials Science and Engineering, Ångström Laboratory, Uppsala University, P.O. Box 35, SE-751 03 Uppsala, Sweden 2Hacettepe University, Department of Physics Engineering, 06800 Beytepe, Ankara, Turkey.

Resume : Materials that are able to vary their transparency and coloration reversibly when they are subjected to an electrical current or voltage are referred to as “electrochromic” (EC). High optical transmittance modulation and long service lifetime are apparent requirements for EC materials used in smart windows technology. An extended service lifetime is provided by the long-term durability of the materials. One important aspect of durability is the ability to sustain charge transport between the EC film and electrolyte, or between the two EC films in a device, for many hundreds or thousands of cycles without any significant changes in the performance such as optical modulation and inserted-extracted charge. The purpose of this study is to clarify the effects of the oxygen-argon gas flow ratio during sputter deposition on the durability of WO3 films. In this study, the oxygen to argon gas-flow ratio was modulated by setting the O2 flow rate to 7.5, 15.0, 22.5, and 45.0 ml min-1 and using a fixed Ar flow rate of 50 ml min-1. Thus, the oxygen to argon gas-flow ratio was varied from 0.15 to 0.90. The pressure in the sputter plasma was set as 30 mTorr and the sputter power was maintained at 200 W. For durability studies, cyclic voltammetry data were recorded for up to 500 cycles between 2.0 and 4.0 V versus Li/Li+ at a scan rate of 20 mV s-1. High oxygen to argon gas ratio was found to have a positive effect on the EC properties of the films. When the long-term performance of the films was examined, it was seen that all the samples displayed a slow decline of the colored-state transmittance due to ion accumulation in the host material. After 500 color-bleach cycles, the maximum optical transmittance modulation between colored and bleached states at a wavelength of 528 nm was 63.6% when the oxygen to argon gas-flow ratio was 0.90.

Authors : Gamze Atak, İlknur Bayrak Pehlivan, José Montero, Claes G. Granqvist, Gunnar A. Niklasson.
Affiliations : Gamze Atak1,2; İlknur Bayrak Pehlivan1; José Montero1; Claes G. Granqvist1; Gunnar A. Niklasson1. 1Department of Materials Science and Engineering, Ångström Laboratory, Uppsala University, P.O. Box 35, SE-751 03 Uppsala, Sweden 2Hacettepe University, Department of Physics Engineering, 06800 Beytepe, Ankara,

Resume : In electrochromic (EC) applications, annealing is a crucial parameter not only for an individual layer but also for a full device. For the fabrication of a complete EC device, indium tin oxide (ITO) is often preferred as a transparent conductor layer. ITO films with high transparency and low electrical resistance are usually obtained by sputtering at high substrate temperatures. Consequently, the effect of high temperature on the EC layers can be very significant during sputtering of the ITO top layer for EC devices consisting of five sputtered layers on a single substrate. The role of annealing of a single layer of WO3 may also be important for EC performance. In the present work, we studied the effects of annealing on the durability of WO3 films. Thin films of WO3 were deposited by reactive DC magnetron sputtering in a mixture of Ar and O2 gases using an oxygen to argon ratio of 0.15. The total gas pressure was set to 4.0 Pa, and the sputtering power was 200 W. The WO3 films were deposited onto (i) unheated glass plates, (ii) such plates pre-coated with transparent and electrically conducting ITO with a sheet resistance of 60 Ω/square, and (iii) glass plates pre-coated with fluorine-doped tin oxide (FTO) with a sheet resistance of 14 Ω/square. Film thicknesses were 300±10 nm. After deposition of the films, the samples were annealed at 150, 300, 450, and 600 °C in ambient air for one h using a heating rate of 10 °C min-1. Cyclic voltammetry (CV) was performed for up to 500 cycles between 2.0 and 4.0 V vs. Li/Li+ at a scan rate of 20 mV s–1. Annealing at temperatures at and above 300 °C resulted in deteriorated electrochromic properties of the WO3 films i.e., a decreased transmittance variation. Charge density and coloration efficiency changes during extended electrochemical cycling were also observed as a function of cycle number and annealing temperature. It was found that the maximum optical transmittance modulation at a wavelength of 528 nm after 500 CV cycles was 69.3% for the film annealed at 150 °C.

Authors : Shangpu Liu1, Gregor Kieslich2, Markus Heindl1, Natalie Fehn2, Aras Kartouzian2, Ian Sharp1, Felix Deschler1
Affiliations : Walter Schottky Institut and Physik-Department, Technische Universität München1 Fakultät für Chemie, Technische Universität München2

Resume : Hybrid organic inorganic perovskites are optoelectronic materials with tunable chemical and electronic structures. Incorporating chiral organic molecules into perovskite networks also attracts great attention due to their potential optical communication applications. Nevertheless, most reported chiral perovskite materials possess high toxic Pb, which potentially limits their practical applications. Here, we introduce chiral organic molecules R/S-1-cyclohexylethylamine (R/S-CHEA) into lead-free bismuth based materials with perovskite motif, and grow color tunable chiral lead-free (R/S-CHEA)4Bi2BrxI10-x (x = 0 to 10) crystals and thin films. We perform single crystal XRD measurement and DFT calculation to identify their crystal structure and electronic band structure. We further investigate their optical properties. We find the absorption peak position is shifted from 386 nm to 493 nm, while Circular Dichroism (CD) signals can be turned widely from 366 nm to 535 nm, by changing the ratios of bromide and iodide anions in (R/S-CHEA)4Bi2BrxI10-x. Specifically, we employ steady-state and time-resolved PL spectra measurements on (R-CHEA)4Bi2Br10 film, which has a broad emission peak located at around 520 nm and shorter lifetime compared with that of Cs2AgBiBr6. Besides, temperature and fluence dependent time-resolved PL spectra are also performed to investigate the charge carrier dynamics in (R-CHEA)4Bi2Br10. Our demonstration of color tunable chiral lead-free perovskites gives the possibility to discover high performance and nontoxic optical spintronic materials.

Authors : Gökhan Gizer, Claudio Pistidda, Thomas Klassen, Martin Dornheim
Affiliations : Helmholtz-Zentrum Hereon, Institute of Materials Technology

Resume : Li-B-N-H systems composed of LiNH2 and LiBH4 are attractive hydrogen storage systems since they are capable of releasing high amount of hydrogen. For example, Li3BN2H8, a milling product of 2LiNH2 and LiBH4, is capable of releasing more than 10 wt % of hydrogen at a temperature range of 250-350 °C. However, main issue is the reversibility of these systems. In this work, experimental results related to hydrogen absorption trials of Li3BN2, which is the desorption product of Li3BN2H8, will be presented at hydrogen pressures up to 2000 bar.

Authors : Higor Andrade Centurion,(1) Renato Vitalino Gonçalves (1)
Affiliations : (1) São Carlos Institute of Physics, University of São Paulo, PO Box 369, 13560-970 São Carlos, SP, Brazil

Resume : The water splitting process using sunlight and particulate photocatalyst to produce H2 fuel, plays an important role in the renewable energy scenario, due to hydrogen as high energy density per m3, easily storable and free of CO2 emission. The SrTiO3 is semiconductor with suitable properties to perform photocatalytic H2 evolution reaction. Their well-knowing wide bandgap (~3.2 eV) and recombination rate of electrons and hole photogenerated limit its photocatalyst activity only for UV-light. In this work, Mo doped SrTiO3 particles were synthesized by molten salt method, resulting in a photocatalyst 4-folds active than the pristine SrTiO3. To suppress the charge recombination, Ni nanoparticles were deposited on the SrTiO3 surface by modified DC magnetron sputtering, leading to H2 evolution rate of 15 umol h-1 under simulated sunlight (AM 1.5G filter). Surprisingly, the optimized Mo:STO@Ni material presented photocatalytic activity under visible irradiation. The UV-Vis absorption confirms the presence of an absorption band in the visible region, associated with an intergap electronic state, induced by the substitution of Ti(IV) ions to Mo(VI) ions. Furthermore, the valance band spectra measured by XPS suggesting an increment of the n-type character of the material, associated with the Mo doping in SrTiO3. The modifications induced by the molybdenum doping and Ni cocatalyst were responsible for an increment of 34-fold in the photocatalytic activity for H2 evolution then pristine SrTiO3.

Authors : Romualdas Jonas Cepas*(1), Kristijonas Genevicius (1).
Affiliations : (1) Institute of Chemical Physics, Vilnius University, Sauletekio al. 3, Vilnius 10257, Lithuania

Resume : Organic small molecule or polymer materials are often used as hole transporting layers (HTLs) in organic optoelectronic devices or perovskite solar cells because of solution processability and tunable optoelectronic properties by chemical structure modification. In comparison to polymer-based HTLs, small molecule based HTLs have the advantage of straightforward purification and batch-to-batch reproducibility. Pyrene, thiophene, porphyrin, and carbazole derivative based HTLs boast high device performance, while carbazole derivatives show good chemical and environmental stabilities, and strategic sites for functional group attachments [1, 2]. In this work we present the study of novel small molecule hole transporting materials based on carbazole and fluorene. Temperature dependent measurements of bimolecular recombination rate and mobility were made in room and below ambient temperatures using time-of-flight (TOF) technique. We also employed extraction of injected charge carriers technique to measure carrier concentration dependent recombination, which allowed us to determine dominant recombination mechanisms. The aforementioned use of this method is novel and was tested on the presented HTL’s to investigate recombination processes and also to compare the results with TOF data. References 1. Bakr, Z. H. et al. Advances in hole transport materials engineering for stable and efficient perovskite solar cells. Nano Energy 34, 271–305 (2017). 2. Prachumrak, N. et al. Novel bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole end-capped with carbazole dendrons as highly efficient solution-processed nondoped red emitters for organic light-emitting diodes. ACS Appl. Mater. Interfaces 5, 8694–8703 (2013).

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A-5 : Rajeev Ahuja, Uppsala University
Authors : Peter Müller-Buschbaum
Affiliations : Technische Universität München, Physik-Department, Lehrstuhl für Funktionelle Materialien, James-Franck-Str. 1, 85748 Garching, Germany

Resume : Based on novel organic semiconductors, organic solar cells are an interesting alternative to conventional silicon based solar cells as they feature new possibilities. Using wet chemical processing, they can be manufactured with large-scale production methods such as roll-to-roll printing. However, in terms of large-scale usability, one of the major challenges for organic solar cells is to overcome their relatively short lifetime, as compared to their inorganic counterparts. To gain a deeper understanding of organic solar cell degradation with respect to changes in the active layer morphology, we present operando studies during the first hours of operation. The studies reveal information on both, its evolving current-voltage characteristics and the changes of the active layer morphology in the organic solar cells. For that purpose, GISAXS / GIWAXS measurements and current-voltage (IV) tracking of the operating solar cell are performed simultaneously to gain fundamental understanding. Starting from an optimized morphology of the active layers in terms of highest device efficiencies, depending on the donor-acceptor organic semiconductor system, different morphological degradation pathways are identified. A mixing or demixing process can occur and cause changes of the active layer morphology. The altered morphology is less optimal for charge transport through the active layer due to poor percolation in a too fine morphology or a poor splitting of excitons in a too coarse morphology.

Authors : Shuqian Zhang
Affiliations : Shanghai Jiao Tong University

Resume : In recent years, solar interfacial evaporation has been one of the most promising techniques to alleviate freshwater scarcity. However, the salt deposition on the evaporation surface limits the long-term operation of evaporators. Herein, inspired by the salt dilution and secretion mechanisms in halophytes, a solar evaporator with a bundle-cross-layer structured absorber and salt secretion bundles is reported. The unique bundle-cross-layer structure realizes the salt dilution by enhancing the water storage and transport, which enables the absorber a high and stable evaporation efficiency of 90.2% over 60 h in brine. More importantly, the salt secretion bundles can completely separate salt crystallization from the absorber by a humidity-controlled salt creeping mechanism. The solar desalination prototype equipped with this evaporator exhibited a stable water collection rate over 600 h of continuous operation, realizing zero liquid discharge in desalination. The study provides new insights into the solar evaporator design and advances other applications such as sea-salt extract, wastewater treatment, and resource recovery.

Authors : Kangkang Zhou, Yanhou Geng, and Long Ye
Affiliations : School of Materials Science and Engineering, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin, 300350, China,

Resume : Record-breaking organic solar cells (OSCs) based on blends of polymer donors and small molecule acceptors often show undesirable degradation, which severely precludes their practical use. Herein, we demonstrate a facile and cost-effective approach to construct thermally stable OSCs at 150 ºC by incorporating a small amount of a polymer insulator polyacenaphthylene (PAC) with high glass-transition temperature over 230 ºC into polymer:acceptor blends. The model PTB7-Th:EH-IDTBR blend with 10 wt% PAC maintained above 85% of its initial efficiency upon continuous heating at 150 ºC for over 800 hours, while the efficiency of the blend without PAC sharply dropped by 70% after ~300 hours. Owing to high miscibility with acceptors, PAC confines the motion of the acceptor molecules and suppresses the acceptor crystallization at elevated temperatures, leading to significantly improved stability. Importantly, the effectiveness of this blending approach was also validated in many other OSC systems, showing great potential for achieving high-performance thermally stable electronics.

Authors : Salvatore La Manna,1, Fiorella Tringali,2, Antonio Terrasi,2, Maria Miritello,1
Affiliations : 1. CNR-IMM, Via S. Sofia,64, I-95123 Catania, Italy 2. University of Catania, Via S. Sofia,64, I-95123 Catania, Italy

Resume : stacks of intrinsic and doped hydrogenated amorphous silicon (a-Si:H) as passivating and carrier-selective layers. These stacks provide good surface passivation and selectivity thanks to the high hydrogen content and dopability of amorphous silicon, respectively. However, some drawbacks limit the cell efficiency, such as the lower conductivity of doped a-Si:H compared to crystalline silicon, low band offsets between these two crystalline phases, parasitic absorption below 500 nm due to the a-Si:H bandgap of about 1.7 eV. An interesting alternative to the doped Si:H layers is the transition metal oxide, owing to the high transparency in the ultraviolet-visible region, the high band gap and the high work function. In particular, substechiometric Molibdenum oxide, having work function higher than 6 eV and bandgap higher than 3 eV, and guaranteeing also a good passivation of silicon, represents a promising material as a hole-selective membrane, that simultaneously can limit the electrons diffusion and facilitate the holes conduction. The transparency and the conductivity of the layer are ruled in particular by presence of oxygen vacancies within the oxide lattice. Indeed, these vacancies generate defect levels in the energy gap which act as donor centers, thus increasing the free carriers. Moreover, the electron barrier is ruled by the MoO3-x work function that is strongly dependent on oxide stoichiometry. Therefore, the challenge is to find the right x value which balances the material properties to maximize its efficacy as hole selective contact. In this study, we synthesize substechiometric Molybdenum oxide, MoO3-x, thin films by UHV magnetron sputtering of an oxide target, and by controlling the film stoichiometry by the argon sputtering pressure. By increasing pressure, x value has been recorded to decrease from 0.25 to 0 by Rutherford Backscattering Spectrometry. Then, the optical characterization has been performed by spectrophotometer in the range 250-2500 nm and the electrical characterization by four point alignment probe and by current-tension curves. The correlation between stoichiometry, and thus oxygen vacancies, and the optical and electrical properties will be clearly showed. In particular, we will evidence the absorption of a peak corresponding to defect levels in the MoOx energy bandgap, related to oxygen vacancies, that decreases by decreasing x value. At the same time the electrical resistivity increases, due to the free carriers increase. The optimal stoichiometry for selective contact application will be discussed, by comparing the characteristics of different prototypes of solar cell having the deposited MoO3-x film as selective contact coupled with a thin Indium Tin Oxide layer.

Authors : Florian Schrenk, Lorenz Lindenthal, Raffael Rameshan, Hedda Drexler, Christoph Rameshan
Affiliations : Institute of Materials Chemistry, Technische Universität Wien, Austria

Resume : Methane dry reforming (MDR) is a reaction utilizing two greenhouse gases, CH4 and CO2, and converting them into valuable synthesis gas. Big scale application of MDR is still hindered by the lack of a durable catalyst. The Ni and Co based catalysts used are often prone to coking and sintering [1]. A possibility to overcome these problems is the use of perovskite type oxide catalysts. Perovskite type oxides have the general formula ABO3. The A, as well as the B, site can be doped thus improving the properties of the catalyst. In our studies the A-site was made up from Nd and Ca. This mixture combines the good redox activity of Nd with the improvement of the defect chemistry brought into play by Ca. The B site was Fe, doped with different amounts of catalytically highly active Ni and Co. If the perovskite is exposed to reducing conditions these catalytically active metals can migrate to the surface, forming metallic nanoparticles [2]. These exsolved nanoparticles have shown to exhibit an increased resistance to sintering as well as coking [3]. We studied the behaviour of Ni and Co doped catalysts during the reaction with operando X-Ray Diffraction (XRD), in-situ near ambient pressure X-Ray Photoelectronspectroscopy (NAP-XPS) as well as catalytic tests. The aim was to assess if and when nanoparticles are formed during the reaction and how a reductive pretreatment is influencing the formation. The combination with Scanning Electron Microscopy (SEM) allowed us to characterize the exsolved nanoparticles regarding their size. The Ni doped variant of the catalyst was more active than the Co doped variant. The XRD experiments showed, the formation of a metallic phase during MDR at elevated temperatures. XPS results confirmed this behaviour and proved that the exsolution was indeed the dopants, Co and Ni, and not Fe. An analysis of the effect of an additional reductive pretreatment revealed an increase in catalytic activity by a huge margin. The main difference between in-situ exsolution and the reductive pretreatment was observed in the SEM images. The reductive pretreatment led to the formation of bigger nanoparticles. This bigger nanoparticles in turn led to an increase in catalytic activity, hinting to a correlation of nanoparticle size and catalytic activity. References: 1. Pakhare, D.; Spivey, J., Chemical Society Reviews 2014, 43 (22), 7813-7837. 2. Lindenthal, L.; Ruh, T.; Rameshan, R.; Summerer, H.; Nenning, A.; Herzig, C.; Loffler, S.; Limbeck, A.; Opitz, A. K.; Blaha, P.; Rameshan, C., Acta Crystallographica Section B-Structural Science Crystal Engineering and Materials 2020, 76, 1055-1070. 3. Neagu, D.; Oh, T. S.; Miller, D. N.; Menard, H.; Bukhari, S. M.; Gamble, S. R.; Gorte, R. J.; Vohs, J. M.; Irvine, J. T. S., Nature Communications 2015, 6. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 755744 / ERC - Starting Grant TUCAS)

Authors : layers Costa, I.(1), Gaspar, G.(1), Serra, F.(1), Guerra, A.(1), Pera, D.(1), Marques, A.C.(2), Ferreira, I.(2), Silva, J.A.(1), Lobato, K.(1), Silva, R.C(3) and Serra, J.M*(1)
Affiliations : (1)Instituto Dom Luiz, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal (2)CENIMAT/I3N, Departamento de Ciência dos Materiais, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal (3) IPFN-IST/UL, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Estrada Nacional 10, 2695-066, Bobadela, Portugal

Resume : Today, most commercial crystalline silicon solar cells are double side contacted cells with conventional junctions and conversion efficiencies around 22 %, limited by recombination losses at the contacts. Passivation contacts have been applied to solar cells and proved to be able to overcome the efficiency bottleneck related to recombination. A big advantage is that they can passivate the entire surface of the wafer instead of localized regions. The current study shows the progress carried out in the development of SiO2/TiO2 passivating contacts for advanced silicon solar cells. To obtain a SiO2 layer in the order of 2 nm, to act as a tunnel effect barrier, dry thermal oxidation has been carried out in a tubular furnace. Several test oxidations were conducted and correlated with simulation predictions for equivalent conditions on silicon (100) [1], and then compared with ellipsometry measurements. As predicted, SiO2 thickness increases with oxidation time and temperature, through with an offset potentially justified by the pre-existing native oxide layer already measuring 1.4-2.5 nm. An e-beam evaporation system was used to stack 10 nm of TiO2 on top of the tunnel effect layer. With the aim of varying the TiO2 layer composition and interface properties, an equivalent group of samples was produced with a stack composed of an extra thin 1 nm layer of Ti over SiO2. The full stacks were finished with an ITO transparent contact for electrical probing. Raman spectroscopy analysis confirm the presence of ITO and its composition homogeneity though the contact, having the characteristic peak centered at 113 cm-1. Raman mapping was performed over the sample surface in areas of 5x5 µm2 and centered in the transition between ITO and TiO2. The two regions are clearly distinguishable from the composition point of view while presenting a sharp interface. Due to the high intensity of the Si/SiO2 peak, and reduced layer thicknesses, further dedicated experiments are being conducted to confirm the TiO2 phase after forming gas annealing. Minority carrier lifetimes were measured, and advanced electrical characterization of the samples is being performed to assess the impact of changes in the TiO2 properties and related interfaces. The authors would like to acknowledge the financial support of FCT through projects: UIDB/50019/2020 ? IDL and PTDC/CTM-CTM/28860/2017. [1] In Semiconductor materials and process technology handbook / edited by Gary .E. McGuire (pp. 48-57).

Authors : Salim Mejaouri(1,2), Stéfania Cacovich(1,3), Mohammad Ali Akhavan Kazemi(4), Fréderic Sauvage(4), Dominique Loisnard(5), Jean Rousset(1,2), Stéphane Collin(1,6)
Affiliations : 1 IPVF, Institut Photovoltaïque d’Ile-de-France, 18 Boulevard Thomas Gobert, 91120 Palaiseau, France 2 EDF R&D, 7 boulevard Gaspard Monge, 91120 Palaiseau, France 3CNRS, École Polytechnique, IPVF, UMR 9006, 18, Boulevard Thomas Gobert, 91120 Palaiseau, France 4 LRCS, Laboratoire de Réactivité et Chimie des Solides – Institut de Chimie de Picardie Université de Picardie Jules Verne, 33 rue Saint Leu, Amiens 8039, France 5 EDF Lab Les Renardières, Avenue des Renardières, 77250 Écuelles, France 6C2N, Centre de Nanosciences et de Nanotechnologies , 10 Boulevard Thomas Gobert, 91120 Palaiseau

Resume : Owing to their remarkable characteristics, lead halide perovskites (LHP) offer new possibilities to outreach efficiency limits of photovoltaic devices. After a decade of optimizing LHP composition, researchers aim at improving their long-term stability. Methodic tests coupling different stress factors have enabled step-by-step improvement of the device stability, but in-depth knowledge of degradation mechanisms and resulting phases are still lacking. In the present work, we investigate the chemical and structural evolution of hybrid cation mixed halide perovskite at different scales through Photoluminescence (PL), Xray Diffraction Spectroscopy (XRD), Energy Dispersive X-ray Spectroscopy (EDS), and Cathodoluminescence (CL) analysis. We first study triple cation perovskite thin films (Cs0.05MA0.45FA0.5Pb(I0.95Br0.05)3) aged under controlled humidity. Structural (XRD) and chemical (EDS) analyses performed during aging reveal details on the degraded phase’s nature. We found a majority of PbI2, as expected, together with lead-rich inorganic phases CsPb2(Br,I)5. CL, as a highly localized optical measurement, yields responses from the different phases in the material separately. According to reference [1], perovskite emission is expected to redshift during aging due to halide segregation. However, we report here the opposite trend with a blue shift of the perovskite response with degradation. We discuss these results and draw a novel portrait of LHP’s evolution when subject to moisture. Second, we investigate powders of lead-rich inorganic compounds. These materials have raised interest as promising optoelectronic materials, but also as a dopant to enhance inorganic LHP thin film stability [2]. We report here their characterization by CL and PL measurements. Our results are in good agreement with the literature for CsPb2I5, but it remains unclear for CsPb2Br5 which demonstrates a high-energy response. A debate on the origin of its green emission is ongoing. Thus, this work comes to feed experimental studies on this controversial subject. Based on these results, we discuss the presence of lead-rich inorganic compounds in the degraded phases of perovskite films. Our results provide insight in the degradation mechanisms of perovskite thin-films and will help a better optimization of materials and device performances. [1] E. T. Hoke, D. J. Slotcavage, E. R. Dohner, A. R. Bowring, H. I. Karunadasa, and M. D. McGehee, ‘Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics’, Chem. Sci., vol. 6, no. 1, pp. 613–617, 2015, doi: 10.1039/C4SC03141E. [2] S. Caicedo-Dávila et al., ‘Effects of Postdeposition Annealing on the Luminescence of Mixed-Phase CsPb2Br5/CsPbBr3 Thin Films’, J. Phys. Chem. C, vol. 124, no. 36, pp. 19514–19521, Sep. 2020, doi: 10.1021/acs.jpcc.0c06955.

10:15 Q&A live session / Break    
A-6 : Rajeev Ahuja, Uppsala University
Authors : Chris G. Van de Walle
Affiliations : Materials Department, University of California, Santa Barbara, California, USA

Resume : Halide perovskites offer impressively high solar conversion efficiencies and are being considered for applications as light emitters. These materials are often called “defect tolerant”, but we show that the impact of point defects on device efficiency has not been properly assessed to date. We have performed comprehensive studies for the prototypical hybrid perovskite MAPbI3 [MA=(CH3NH3)], as well as for other halide perovskites. To achieve accurate and reliable results, our first-principles calculations are based on hybrid density functional theory with spin-orbit coupling included [1]. Rigorous calculations of nonradiative recombination coefficients show the limitations of the widely adopted rule that only defects with charge-state transition levels deep in the band gap can be efficient nonradiative recombination centers. We demonstrate that the position of the level does not directly determine the capture rates, due to exceptionally strong lattice coupling and anharmonicity in the halide perovskites [2]. Our results clearly show that (1) point defects can indeed be present in relevant concentrations in the halide perovskites and (2) some of these point defects lead to nonradiative recombination rates that are just as high as in conventional semiconductors. We therefore conclude it is incorrect to call the halide perovskites “defect tolerant”. A more relevant distinction, compared to conventional semiconductors, is that halide perovskites with modest defect densities can be grown using low-cost deposition techniques. Finally, we show that point defects associated with the methylammonium molecule can act as strong nonradiative recombination centers, and we provide guidance for how this can be suppressed. Work performed in collaboration with X. Zhang, M. Turiansky, and J.-X. Shen. [1] X. Zhang, M. E. Turiansky, J.-X. Shen, and C. G. Van de Walle, Phys. Rev. B 101, 140101 (2020). [2] X. Zhang, M. E. Turiansky, and C. G. Van de Walle, J. Phys. Chem. C 124, 6022 (2020). [3] X. Zhang, J.-X. Shen, M. E. Turiansky, and C. G. Van de Walle, Nat. Mater. 20, 971 (2021). Work supported by DOE.

Authors : Seán R. Kavanagh,[1,2] Aron Walsh,[2,3] David O. Scanlon[1,4]
Affiliations : 1 - Thomas Young Centre and Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K; 2 - Thomas Young Centre and Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K; 3 - Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea; 4 - Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, U.K.

Resume : The ability to accurately model, understand and predict the behaviour of crystalline defects would constitute a significant step towards improving photovoltaic device efficiencies and semiconductor doping control, accelerating materials discovery and design.1 In this work, we apply hybrid Density Functional Theory (DFT) including spin-orbit coupling to accurately model the atomistic behaviour of the cadmium vacancy (VCd) in cadmium telluride (CdTe).1 In doing so, we resolve several longstanding discrepancies in the extensive literature on this species. CdTe is a champion thin-film absorber for which defects, through facilitation of non-radiative recombination, significantly impact photovoltaic (PV) performance, contributing to a reduction in efficiency from an ideal detailed-balance limit of 32% to a current record of 22.1%. Despite over 70 years of experimental and theoretical research, many of the relevant defects in CdTe are still not well understood, with the definitive identification of the atomistic origins of experimentally observed defect levels remaining elusive.2–4 In this work, through identification of a tellurium dimer ground-state structure for the neutral Cd vacancy, we obtain a single negative-U defect level for VCd at 0.35 eV above the VBM, finally reconciling theoretical predictions with experimental observations. Moreover, we reproduce the polaronic, optical and magnetic behaviour of VCd-1 in excellent agreement with previous Electron Paramagnetic Resonance (EPR) characterisation.5,6 We find the cadmium vacancy facilitates rapid charge-carrier recombination, reducing maximum power-conversion efficiency by over 5% for untreated CdTe—a consequence of tellurium dimerisation, metastable structural arrangements, and anharmonic potential energy surfaces for carrier capture. The origins of previous discrepancies between theory and experiment, namely incomplete mapping of the defect potential energy surface (PES) and approximation models, are highlighted and discussed. Importantly, these results demonstrate the necessity to include the effects of both metastability and anharmonicity for the accurate calculation of both charge-carrier recombination rates in emerging photovoltaic materials and the efficiency limits imposed by both native and extrinsic defect species. 1 Y.-T. Huang, S. R. Kavanagh, D. O. Scanlon, A. Walsh and R. L. Z. Hoye, Nanotechnology, 2021, 32, 132004. 2 S. R. Kavanagh, A. Walsh and D. O. Scanlon, ACS Energy Lett., 2021, 6, 1392–1398. 3 A. Lindström, S. Mirbt, B. Sanyal and M. Klintenberg, J. Phys. D: Appl. Phys., 2015, 49, 035101. 4 J.-H. Yang, W.-J. Yin, J.-S. Park, J. Ma and S.-H. Wei, Semicond. Sci. Technol., 2016, 31, 083002. 5 A. Shepidchenko, B. Sanyal, M. Klintenberg and S. Mirbt, Scientific Reports, 2015, 5, 1–6. 6 P. Emanuelsson, P. Omling, B. K. Meyer, M. Wienecke and M. Schenk, Phys. Rev. B, 1993, 47, 15578–15580.

Authors : Nikhar Khanna*(1, 2), Mohamed El-Hachemi(1).
Affiliations : (1) Materials Research and Technology Department, Luxembourg Institute of Science and Technology, Luxembourg. (2) Department of Physics and Material Science, University of Luxembourg, Luxembourg.

Resume : AN ELLIPSOMETRIC ANALYSIS OF A SYNTHESIZED NANOSCALE LAYERED COMPOSITE WITH CONFORMAL COATING OF ALUMINIUM NITRIDE OVER THE DISTRIBUTION OF TITANIUM NITRIDE NANOPARTICLES, FOR CSP APPLICATIONS. Solar-thermal energy conversion is a promising technology that enables efficient energy harvesting from concentrated solar power (CSP). Recently, there is a lot of interest in metal- insulator based metamaterial absorbers due to the complete hold on the permittivity and permeability of these absorbers. The permittivity and permeability lean directly on the optical properties of the material that can be altered by controlling the morphology at the nanoscale. In our case, a part of the metamaterial absorber consists of near homogeneous distribution of nanoparticles (Titanium Nitride, TiN) in a matrix of (Aluminium Nitride, AlN), to form a composite. Electromagnetic wave absorbers have been investigated for many years with the aim of achieving high absorbance and tunability of both the absorption wavelength and the operation mode by geometrical control, small and thin absorber volume, and simple fabrication. The present work involves the synthesis of a composite dielectric of approximately 200 nm thickness where nanostructure control is a very challenging task. In this work, we choose a bottom-up approach of constructing a stack of, TiN nanoparticles distribution over a substrate and then a layer of AlN of 20 nm thickness, and so on. TiN particles are laid over Silicon wafer by wet chemical method and are then coated with a conformal coating of Aluminium Nitride, via Plasma- enhanced Atomic Layer deposition. These components together form the dielectric composite, where each component plays a different role in light absorption. The control of the morphology at the nanoscale is primordial to improve the material?s optical performance, thus in our case maximize the wave extinction inside the composite for the application as a solar absorber. Later, a straightforward and robust method is used to predict the optical properties of the prepared nanostructure, with high accuracy. The optical properties (n, k) of the composite are measured by Spectroscopic Ellipsometer. In order to have composite best suited for our requirement, two types of composites were prepared. One with TiN powder mixed in water as a solvent, and the other with commercially available TiN dispersions, both with a layer of AlN on top, covering the TiN particles. Both the composites were prepared in an identical way with alternate layers of TiN distribution and AlN film until a stack of approximately 200 nm was ready. In both cases, fewer clusters of 200nm to1µm of TiN particles were present however, enough steps were taken to minimize these clusters into smaller particles. In conclusion, the work presented here is the comparison of the two kinds of composites with their optical properties (n, k) measured by the ellipsometer.

Authors : Kargal L Gurunatha, Sanjayan Sathasivam, Jianwei Li, Mark Portnoi, Ivan P. Parkin and Ioannis Papakonstantinou
Affiliations : University College London, United Kingdom.

Resume : Vanadium dioxide (VO2) is a promising material in the development of thermal and electrically sensitive devices due to its first order reversible metal-insulator transition (MIT) at 68 °C. Such high MIT temperature (TC) largely restricts its widespread application which could be enabled if a straightforward tuning mechanism were present. Here this need is addressed through a facile approach that uses the combined effects of temperature induced strain and oxygen vacancies in bulk VO2 colloidal particles. Simple thermal annealing process under varying vacuum is used to achieve phase transformation of metastable VO2 (A) into VO2 (M2), (M2+M3), (M1) and higher valence V6O13 phases. During this process, distinct multiple phase transition including increased as well as suppressed TC is observed with respect to the annealing temperature and varied amount of oxygen vacancies respectively. The latent heat of phase transition is also significantly improved upon thermal annealing by increasing the crystallinity of the samples. This work not only offers facile route for selective phase transformation of VO2 as well as to manipulate the phase transition temperature, but also contributes significantly to the understanding of the role played by oxygen vacancies and temperature induced stress on MIT which is essential for VO2 based applications.

Authors : Cristina V. Manzano1,2*, Olga Caballero-Calero1, Maxime Tranchant2, Enrico Bertero2, Pablo Cervino-Solana1, Marisol Martín-González1, Laetitia Philippe2
Affiliations : 1. Instituto de Micro y Nanotecnología, IMN-CNM, CSIC (CEI UAM CSIC) Isaac Newton, 8, E-28760, Tres Cantos, Madrid, Spain 2. Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures, Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland

Resume : The application of inexpensive and scalable materials in the industry for thermoelectric applications has received great interest, such as CuNi alloys in the last ears. Nanocrystalline CuNi alloys with different compositions were grown by pulsed electrodeposition reducing the crystallite size of the CuNi down to 30-40 nm by the incorporation of saccharine in the electrolyte1,2. The thermoelectric properties, such as electrical conductivity, Seebeck coefficient, and thermal conductivity of these nanocrystalline alloys, were studied. The maximum figure of merit at room temperature obtained was (6.4 ± 1.5) ·10-2 for nanocrystalline Cu0.65Ni0.35. The thermal conductivity of CuNi alloys was reduced by the nanostructuration to a value of 9.0 ± 0.9 W/m·K, making these nanocrystalline CuNi alloys more competitive than other more classical thermoelectric materials. This work opens a new field to be investigated, that can be described as the use of commercial alloys such as CuNi for thermoelectric applications, and shows the use of a new approach to enhance the thermoelectric properties of inexpensive and/or fewer pollutant materials. 1. C. V. Manzano*, O. Caballero-Calero, M. Tranchant, E. Bertero, P. Cervino-Solana, M. Martín González, and L. Philippe. Thermal Conductivity Reduction by Nanostructuration in Electrodeposited CuNi Alloys. J. Mater. Chem. C, 9(10), pp. 3447–3454, 2021. 2. High aspect-ratio nanocrystalline CuNi T-structures and micro-gears: Synthesis, numerical modeling and characterization. Manzano, C.V., Schürch, P., Pethö, L., Bürki, G., Michler, J., Philippe, L. Journal of the Electrochemical Society, 2019, 166(10), pp. E310–E316

Authors : Mohamed Nawfal Ghazzal,1 Jian Li,1 Amine Slassi,2 David Cornil,2 Jérôme Cornil2
Affiliations : 1 Université Paris-Saclay, UMR 8000 CNRS, Institut de Chimie Physique, Orsay, 91405 France 2 Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, Mons, 7000 Belgium

Resume : Solar water splitting into hydrogen is one of the promising means for dealing with energy shortage and environmental problems. H-substituted graphdiyne (H-GDY), for the first time, is employed to fabricate a heterojunction with P25 to improve the photocatalytic activity. The obtained TiO2/H-GDY heterojunctions were characterized by XRD, EDX, TEM, XPS and UV-vis spectrums to ascertain the structure and electronic properties of the composites. Enhanced photocatalytic properties were demonstrated for the as-prepared samples. The influence of the H-GDY content on the photocatalytic activity was investigated and all the samples showed enhanced photocatalytic activity. The amount of hydrogen by the optimized heterojunctions was ~370 mmol after 6 hours test, much higher than that of pristine P25. Such enhancement was ascribed to the H-GDY/P25 heterojunction structure, which can simultaneously improve the absorption of visible light and facilitate the photo-excited electron?hole separation during the photocatalytic process. This work opens new perspectives for application of H-GDY in photocatalytic field.

Authors : Ashish Prajapati1, Jordi Llobet3, Patrícia C Sousa4, Helder Fonseca4, Carlos Calaza4, João Gaspar4, Gil Shalev1,2*
Affiliations : 1 School of Electrical Engineering, Ben-Gurion University of the Negev, Israel 2 The Ilse-Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, POB 653, Beer-Sheva 8410501, Israel 3 Institut de Microelectrònica de Barcelona (IMB-CNM CSIC), 08193 Bellaterra, Catalonia, Spain 4 Microfabrication and Exploratory Nanotechnology group, International Iberian Nanotechnology Laboratory (INL), Braga, 4715-330, Portugal *corresponding author:

Resume : Omnidirectional absorption is important to non-tracking systems designed for the harvesting of solar energy. Presently, we examine both experimentally and numerically the broadband absorption under oblique illumination driven by deep sidewall subwavelength structures (DSSS) in silicon nanopillar arrays (DSSS arrays). Specifically, we target DSSS geometries that are a built-in side effect of the top-down cyclic Bosch dry etch process employed to realize high aspect ratio silicon nanopillar (NP) arrays. We numerically compare the DSSS array with an optically-optimized straight-sidewall nanopillar array (SSNP array) under oblique illumination. We show how the presence of DSSS generates a higher absorptivity particularly for the spectral range >600 nm, induces the formation of absorptivity peaks at the near-infrared spectral range, and overall provides an enhanced omnidirectional broadband absorption. We experimentally show that the specular reflectivity and the total reflectivity of silicon DSSS arrays that were fabricated using a top-down Bosch dry etch process is significantly lower compared with that of the corresponding SSNP arrays. Specifically, we show a decrement in the broadband specular reflection of up to 30% for certain angles of illumination, and about 13% decrement in the total reflectivity.

13:00 Q&A live session / Break    
A-7 : Wei Luo, Uppsala University
Authors : M. Taeño (1), D. Maestre (1), J. Ramírez-Castellanos (2), P. See Lee (3), A. Cremades (1)
Affiliations : (1)Departamento de Física de Materiales, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040, Spain (2)Departamento de Química Inorgánica I, Facultad de CC. Químicas, Universidad Complutense de Madrid, 28040, Spain (3)School of Materials Science and Engineering, Nanyang Technological University, Singapore

Resume : Supercapacitors have become in one of the most promising energy storage and conversion devices with high power densities. Among the parts of a full supercapacitor device, the electrode is considered the key component which directly affects the electrochemical performance of a supercapacitor. In this context, transition metal oxides and hydroxides have been explored as a material for supercapacitor electrodes due to their high conductivity. Among them, the most commonly used electroactive materials are MnO2, Co3O4, NiO, Co(OH)2 or Ni(OH)2. By controlling the experimental conditions such as morphology, size or composition high-performance supercapacitors can be fabricated. In this work, Sn doped Ni(OH)2 nanostructures have been synthesized following a modified hydrothermal method which allows to control not only the Sn composition but also the formation of α- and β-Ni(OH)2 polymorphs. By controlling the experimental conditions such as Sn concentration, temperature, pH, or time reaction, different Ni(OH)2 polymorphs (α and β) have been obtained as has been confirmed by XRD and Raman spectroscopy. TEM analysis showed that undoped Ni(OH)2 is formed by nanoplatelets with dimensions around hundreds of nm, while Sn incorporation induces the formation of elongated structures in form of nanobars with lengths between 40 and 100 nm. Moreover, compositional mappings showed a homogeneous distribution of Sn for all the doped samples. Electrochemical measurements showed a maximum specific capacitance of 1870 F/g for the sample with lowest Sn content. The superior performance of this sample is attributed to the lower charge resistance confirmed by EID measurements. These results confirm that Sn doped Ni(OH)2 can be considered as alternative active materials with promising applicability as electrode in supercapacitors.

Authors : Shaik Junied Arbaz*, S. Chandra Sekhar, Bhimanaboina Ramulu, Manchi Nagaraju and Jae Su Yu.
Affiliations : Department of Electronics and Information Convergence Engineering, Institute for Wearable Convergence Electronics, Kyung Hee University, 1732 Deogyeong-daero, Gihung-gu, Yongin-si, Gyeonggi-do 17104, Republic of Korea.

Resume : The rapidly depleting fossil resources and an ever-increasing demand for energy consumption around the world have resulted in the need for alternative sustainable and renewable energy resources. Among the developed electrochemical energy storage devices, supercapacitors (SCs) have been attracting a great deal of attention due to their unique features like high power output, rapid charging, and durability. However, the relatively low energy density of SCs still needs to be improved in view of their practical applications. Since active materials are crucial in achieving the high energy density of SCs, one should come up with a nice strategy to prepare them with high theoretical capacity, high redox-active, and good electrical conductive properties. Among the variable materials, bimetallic layered double hydroxides (LDHs) are most notable owing to their promising redox properties as well as facile preparation. In this presentation, we have synthesized the bimetallic LDH nanowires (NWs) directly on carbon cloth using a facile hydrothermal method. Furthermore, a metal sulfide nanolayer was wrapped over these NWs by a simple electrodeposition technique. The as-obtained composite material with redox properties of both bimetallic LDH and metal sulfide exhibited a noteworthy electrochemical response in a three-electrode system. Moreover, a pouch-type hybrid SC was fabricated with this composite material as a positive electrode and activated carbon as a negative electrode, which also demonstrated a superior energy storage performance along with notable energy density.

Authors : B. N. Vamsi Krishna *, Obula Reddy Ankinapalli, and Jae Su Yu.
Affiliations : Department of Electronic Engineering, Institute for Wearable Convergence Electronics, Kyung Hee University, Yongin-si, Gyeonggi-do 17104, Republic of Korea.

Resume : With the issues of global warming, energy crisis, and environmental pollution, there has attracted a lot of attention for developing clean and renewable energy storage/conversion systems, such as fuel cells, supercapacitors, and batteries. In this presentation, the nickel molybdenum phosphide (NMP) nanoparticles supported by graphene sheets directly grown on nickel foam were prepared by a facile hydrothermal method. Moreover, the structure and morphology of NMP-graphene oxide (GO) material were investigated by SEM, XRD, and TEM analyses. The optimized NMP-GO electrode material revealed enhanced specific capacity as compared to pristine NMP. Furthermore, the NMP-GO electrode material delivered an excellent specific capacity of 159 mAh g-1 at a current density of 1 A g-1. The fabricated pouch-like asymmetric supercapacitor (ASC) device exhibited improved rate capability, power density, and energy density as well as ultra-stable cycling performance. Also, various portable electronic devices were powered up using the ASC devices to test real-time applications. Distinctly, the obtained better results strongly suggest that the NMP-GO-based electrode materials are very promising for energy storage applications.

Authors : Kalpana Balaskandan1,2*, Adriana Navarro-Suarez1, Anthony R J Kucernak1 Emile S Greenhalgh3, Milo S P Shaffer1,2.
Affiliations : 1 Department of Chemistry, Imperial College London, London, W12 0BZ, UK. 2 Department of Materials, Imperial College London, London, SW7 2AZ, UK. 3 Department of Aeronautics, Imperial College London, SW7 2AZ, UK

Resume : Fibre-shaped architectures/fibre assemblies have emerged as promising candidates as electrodes for energy storage devices, with improved rate capability and with the potential to out-perform traditional laminate/planar counterparts. Carbon nanotube (CNT) containing fibres have the potential to produce strong and highly electrically conducting devices and allow for a greater control over fibre properties through synthesis. In particular, solution spinning has been proven to be a versatile technique for producing tough, high performance CNT fibres. Fibre properties can be selectively tailored through altering the chemistry in the spinning dope and during the coagulation step in addition to varying the spinning conditions; to attain optimised fibres with maximal electrochemical and mechanical properties [1,2]. CNT-based fibres have been produced using surfactant-containing dispersions [3], by strong acid protonation [4], and via single-walled carbon nanotube (SWCNT) solutions prepared using reductive chemistry [5], producing strong and conductive fibres. In all methods of synthesis, CNT individualisation was critical to producing a high-performance fibre. In this research, neat SWCNT fibres are fabricated by means of solution spinning, serving as microelectrodes for proposed fibre-shaped supercapacitor devices. These fibres are both load bearing and display superior capacitive behaviour (40 F/g in aqueous electrolyte). [1] J. J. Vilatela, R. Marcilla, Tough Electrodes: Carbon Nanotube Fibers as the Ultimate Current Collectors/Active Material for Energy Management Devices, Chem. Mater., 2015, 27 (20), 6901-6917. [2] X. Zhang, et al., Understanding the Mechanical and Conductive Properties of Carbon Nanotube Fibers for Smart Electronics, Adv. Mater., 2020, 32, 1902928 (1-21). [3] B. Vigolo, et al., Macroscopic Fibers and Ribbons of Oriented Carbon Nanotubes, Science, 2000, 290, 1331-1334. [4] L. M. Ericson, et al., Macroscopic, Neat, Single-Walled Carbon Nanotube Fibers, Science, 2004, 305, 1447- 1450. [5] A.J. Clancy, et al., Reductive Dissolution of Supergrowth Carbon Nanotubes for Tougher Nanocomposites by Reactive Coagulation Spinning, Nano, 2017, 9, 8764-8773.

15:00 Q&A live session 1    
Authors : Taisiia Berestok*(1,2,3), Christian Diestel(1,2), Niklas Ortlieb(1,2,3), Jan Buettner(1,2,3), Joel Matthews(1,2,3), Patricia Schulze(4), Jan-Christoph Goldschmidt(4), Stefan W. Glunz(1,4,5,6), Anna Fischer(1,2,3,5).
Affiliations : (1) Cluster of Excellence livMatS @ FIT — Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Germany. (2) Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT), University of Freiburg, Germany (3) Institute of Inorganic and Analytical Chemistry, University of Freiburg, Germany. (4) Fraunhofer Institute for Solar Energy Systems (ISE), Freiburg, Germany. (5) Freiburg Materials Research Center (FMF), University of Freiburg, Germany (6) Department of Sustainable Systems Engineering (INATECH), Freiburg, Germany.

Resume : Energy-autonomous electronic devices (termed Internet of Things, IoT) call for novel integrated systems that are able to harvest, store and release energy. This can be achieved by coupling a photovoltaic energy harvester with a storage unit. The intermittency of the energy source and consumption requires the storage device to operate efficiently under fast charging and discharging conditions, which is a characteristic of a capacitive system but not a battery. In particular, electric double layer capacitors (EDLCs) deliver much faster power output as they do not suffer from slow solid-state diffusion reactions or redox process. An interesting approach to achieve energy autonomy is to combine the IoT device with a photovoltaic (PV) solar cell and a charge storage unit, such as an EDLC. The solar cell converts ambient light into an electric current to charge the storage unit, which then in turn supplies the IoT device. This allows for applications in a wide variety of environments, whether it be outdoors or indoors. Such a hybrid system is usually realised via modular coupling, where a PV cell is wired to an EDLC, using a total of four electrodes (two for the solar cell and two for the storage unit).1 The additional circuitry introduces energy loss, and further downsides include complex packaging and design. We approach this problem by developing a monolithic photorechargeable supercapacitor. It consists of a p-i-n halide perovskite solar cell integrated in a three-electrode configuration with an electrochemical double layer capacitor (EDLC) that has mesoporous N-doped carbon nanospheres (MPNC) as the active electrode material. Due to the large surface area, well-defined mesoporous structure and homogeneous particle size of the MPNC material, the EDLC shows both a high capacitance, resulting in large energy and power densities (3.3 Wh kg 1 and 2.6 kW kg 1 @ 5 mA cm 2) and high (95 %) coulombic efficiency.2,3 Using a sequence of layers that optimizes charge transport while minimising material degradation, we integrated the EDLC with a 12.5 % efficient, large-area (1 cm2) perovskite solar cell. The resulting photosupercapacitor exhibits fast (< 5 s) photocharging up to 1 V under 1 sun illumination and an outstanding overall energy conversion efficiency of 11.8 %. Our results show high potential for such integrated energy-harvesting and storage systems to help pave the way towards energy-autonomous devices. [1] Zeng, Q.; Lai, Y.; Jiang, L.; Liu, F.; Hao, X.; Wang, L.; Green, M. A. Adv. Energy Mater. 2020, 10 (14), 1. [2] Melke, J.; Schuster, R.; Möbus, S.; Jurzinsky, T.; Elsässer, P.; Heilemann, A.; Fischer, A. Carbon N. Y. 2019, 146, 44–59. [2] Melke, J.; Martin, J.; Bruns, M.; Hügenell, P.; Schökel, A.; Montoya Isaza, S.; Fink, F.; Elsässer, P.; Fischer, A. ACS Appl. Energy Mater. 2020, 3 (12), 11627–11640.

Authors : Avinash Vikatakavi*1,2, Stefania Benedetti1, Giulia Righi1,2, Paola Luches1, Sergio D’Addato1,2, Rita Magri1,2, Annabella Selloni3
Affiliations : 1. CNR−Instituto Nanoscienze, 41125 Modena, Italy; 2. Dipartimento di Fisica, Informatica e Matematica, Università di Modena e Reggio-Emilia, 41125 Modena, Italy; 3. Department of Chemistry, Princeton University, Princeton, New Jersey 08540, United States.

Resume : CeO2 is a promising material for many catalytic applications due to its ability to store and release oxygen at ease. The reactivity of ceria towards H2 dissociation can be altered by doping it with cationic species such as Ag, Au and Cu. Ceria doped with such metals reduces the activation energy for the dissociation of H2 and becomes a potential candidate for electrode material in fuel cells. In this work we investigate the reactivity of Cu-modified ultra-thin epitaxial CeO2 films on Pt (111) towards H2 dissociation in UHV conditions. The films are prepared by reactive MBE and XPS is used to study the changes in the oxidation state of Ce ions, O vacancy formation and hydroxyl group formation on the surface after thermal reduction cycles in H2. Cu-modified ceria films showed a higher concentration of Ce3+ after thermal treatments under H exposure and a lower activation temperature (470 K-570 K) than the Ag-modified and pure CeO2 films previously investigated [1]. The observed reactivity of the films is higher in presence of a pure CeO2 buffer layer, due to confinement of Cu atoms on the surface, in agreement with theoretical predictions [2]. A significant increase in OH concentration on the surface is observed with the increase in thermal reduction temperature in H atmosphere. STM results show no significant changes in the surface of Cu-modified ceria films after all reducing thermal treatments. [1] S. Benedetti et al., ACS Appl. Mater. Interfaces 12, 27682 (2020) [2] G. Righi et al. J. Phys. Chem. C 123, (2019) 9875

Authors : Mandar Vasant Paranjape*, Sontyana Adonijah Graham, Harishkumarreddy Patnam, Punnarao Manchi and Jae Su Yu.
Affiliations : Department of Electronics and Information Convergence Engineering, Institute for Wearable Convergence Electronics, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin-Si, Gyeonggi-do, 446-701, South Korea.

Resume : The triboelectric nanogenerator is one of the key technologies to efficiently harvest small-scale mechanical energy into electricity. Moreover, hybridizing triboelectric polymer with piezoelectric materials can enhance the electrical output of nanogenerators. In this regard, an efficient hybrid nanogenerator (HNG) was fabricated using the dopamine (DA) modified tin oxide (SnO2)/PVDF composite films. Initially, the SnO2 particles were synthesized using the hydrothermal synthesis method and their surface with a layer of DA was further modified. It is well known that the SnO2 and PVDF are piezoelectric materials that are efficiently used in nanogenerator fabrication. However, modifying the SnO2 particle surface with DA before loading into the PVDF polymer enhances the composite film properties, resulting in an enhanced electrical output. An HNG was fabricated using the DA modified SnO2/PVDF composite film and operated against PTFE. Furthermore, the effect of DA-SnO2 concentration in the PVDF was systemically studied. The maximum electrical output produced by the HNG is higher than the PVDF and SnO2/PVDF composite film-based HNGs. Additionally, the mechanical stability and durability of the HNG were investigated. To verify the practical applications of the HNG, the mechanical energy available in everyday human life was harvested to power various portable electronics.

15:55 Q&A live session 2    
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A-8 : Rajeev Ahuja, Uppsala University
Authors : Stefano Leoni, Rhiannon Morris, Bo Hou
Affiliations : School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK; 1School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK; School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, UK

Resume : The search for efficient materials for energy conversion and storage critically depends on novel protocols for materials discovery, simultaneously allowing for efficient property prediction, including static and dynamic properties. While crystal structure prediction of dense crystalline materials is reasonably straightforward, finding metastable and porous carbon materials remains a challenge; however, these material are of fundamental importance for energy storage and specifically for Li-ion batteries. Furthermore, better open-framework carbons can be considered for larger ions, simplifying the technology transfer from Li- to Na-based batteries. Here we demonstrate a novel strategy for crystalline and porous carbon framework prediction, which can facilitate the discovery and synthetic design of novel carbons. Therein, the concept of tiling of an underlying 2D, hyperbolic manifolds is used as a mathematical guidance to design frameworks ab initio, leveraging topological enumeration measured by the surface genus. Overall, a large number of carbons can be suggested, with important applications in transport and energy storage, including even nanoelectronics, due to distinguished, low-dimensional electronic properties. This large class of gaphenoid structures is demonstrated to perform well as Li or post-Li intercalation material by molecular dynamics simulations.

Authors : Ning Mao1, 2, ;Teng Zhang3, ;Zhirong Wang1*, ;Qiong Cai2*
Affiliations : 1Jiangsu Key Laboratory of Urban and Industrial Safety, College of Safety Science and Engineering, Nanjing Tech University, Nanjing 210009, China 2Department of Chemical and Process Engineering, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom 3Department of Mechanical Engineering Science, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom 

Resume : Overcharge of lithium-ion batteries (LIBs) not only causes irreversible battery degradation and failure but can also trigger disastrous thermal runaway. This paper presents a systematic investigation of the electrical and thermal behaviors of LIBs during overcharge up until thermal runaway, and reveals the underlying physical, structural, and chemical changes at each electrode at different stages of overcharge using microscopic and spectroscopy characterizations. The overcharge process for LIBs with Li(Ni0.6Mn0.2Co0.2)O2 cathode can be divided into four stages: Stage I involves the decomposition of LiMnO2 into MnO and LiNiO2 into NiO, accompanied by a slight collapse of the cathode. In stage II, the cathode forms a relatively stable hexagonal phase H3 while lithium plating occurs on the anode surface. NiO and Ni(OH)2 decompose into metallic Ni and release a lot of heat. In stage III, MnO2 is present on the cathode which is irreversibly damaged, and an unstable substance LiH is produced on the anode that accelerates the onset of thermal runaway. In stage IV, the battery ruptures at approximately 174 % state of charge (SOC), followed by thermal runaway in just 20 s. During overcharge, the crystallinity of the cathode is found to be linearly corelated with SOC.

Authors : Stolyarova S.G*., Fedoseeva Y. V., Shlyakhova E. V., Vorfolomeeva A.A., Grebenkina M.A., Okotrub A.V., Bulusheva L.G.
Affiliations : Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia

Resume : The expansion of the field of applications of lithium-ion batteries as power sources and the future problem of limited lithium resources requires the development of new electrode materials with high capacity and energy density, but also replacement of lithium with cheaper and abundant sodium [1]. Simple substitution of lithium to sodium is impossible due to some problems. Also, standard graphitic anode materials for lithium-ion batteries are not suitable for use in sodium-ion batteries (SIBs) of the low capacity and absence of intercalation. However, different defects (vacancies, atom-dopants) in graphene planes and large interplanar distance promotes sodium intercalation. Among carbon materials, porous carbons (PCs) have a developed surface and the presence of pores, into which they can serve as additional pathways for sodium diffusion and adsorption. In our work, we propose to use brominated nitrogen-doped porous carbon as anode material for SIB. Nitrogen-doped carbon materials have proven themselves for lithium and sodium ion storage, and bromination can introduce the C-Br group affecting the capacity of PCs. At the first stage, porous nitrogen-doped carbon materials (N-PC) were synthesized by acetonitrile vapor deposition on the products of thermolysis of calcium tartrate, adipate, and glutarate at different synthesis temperature 650-850 °C to optimize the synthesis conditions and select the optimal material morphology for anodes SIB. Based on the results of testing and studying the composition and structure of the samples, a synthesis temperature of 750 °C was chosen. N-P?s were brominated using molecular bromine at room temperature. The study of the electronic state of the samples showed that in all porous carbons, bromine is contained in two main forms ? intercalated molecular bromine (Br2 and Brn) and covalent C-Br bonds. N-PC synthesized using calcium tartrate after bromination demonstrated the best performance in SIB of 245 mAhg-1 at 0.1 Ag-1, which is 40% more than the capacity of the original N-PC. Cyclic voltammetry and electrochemical impedance spectroscopy studies have shown that bromine is involved in the accumulation of sodium ions at different potentials 1.5 and 2.1 V for C-Br and Brn species, respectively. In conclusion, the bromination of nitrogen-doped porous carbons is an effective technique for improved sodium-ion storage performance. The work was conducted with financial support from the Russian Science Foundation (Grant 19-73-10068). References 1. A.A. Fedosova, S.G. Stolyarova, Y. V. Shubin, A.A. Makarova, A. V. Gusel?nikov, A. V. Okotrub, L.G. Bulusheva, Sodium storage properties of thin phosphorus-doped graphene layers developed on the surface of nanodiamonds under hot pressing conditions, Fullerenes Nanotub. Carbon Nanostructures. 28 (2020) 335?341.

Authors : Agnieszka Chojnacka, Xuexue Pan, François Béguin
Affiliations : Poznan University of Technology Institute of Chemistry and Technical Electrochemistry Berdychowo 4, 60-965 Poznan, Poland

Resume : The rapid technological development of electric vehicles and large-scale energy storage technologies requires electrochemical devices with a high energy and power metrics Such parameters can be delivered by hybrid metal-ion capacitors (MICs), which combine the advantages of metal-ion batteries (MIBs) and electrical double layer capacitor (EDLCs), by incorporating a highly porous EDL electrode (from activated carbon – AC) and a battery-type anode where alkali ions are reversibly inserted/deinserted. Nonetheless, one of the main issues existing in the development of MICs is the finding of an appropriate pre-metallation method of the anodic host. A recently suggested strategy is to incorporate sacrificial metal oxides or metal salts (from which metal ions can be irreversibly extracted and transferred to the negative electrode by electrochemical oxidation) in the positive electrode [1-4], leading to the realization of the MICs. However, the sacrificial materials should fulfill four important criteria: (i) exhibit a low extraction potential of the metallic ions to limit the risks of electrolyte oxidation; (ii) display a high irreversible capacity to reduce as much as possible the eventually remaining dead mass; (iii) should be stable in air for the easiness of electrodes manufacturing; and (iv) the residue should preferably be an inert gas or eventually a neutral liquid which remains dissolved in the electrolyte. Since squarates offer the essential advantage of stability in air - resulting in the simplification of the electrodes fabrication, as well as an oxidation potential ca. 4.0 V vs. Na/Na+ [4], our objective was to better identify the oxidation products of Na2C4O4 and further to incorporate it in AC-Na2C4O4//Sn4P3 cells for the presodiation of the Sn4P3 alloy anodic material, and thereof realize Na-ion capacitors (NICs). The irreversibility of sodium extraction was confirmed by cyclic voltammetry and galvanostatic charge/discharge, with a capacity of 342 mAh g-1, close to the theoretical one of 339 mAh g-1. Remarkably, the gaseous oxidation products of the C4O42- anion were identified as CO and CO2 by operando electrochemical mass spectrometry, whereas the presence of carbon blended in the electrode (produced by the disproportionation of CO) was proved by Raman spectroscopy and nitrogen adsorption/desorption at 77 K. The NICs resulting from the oxidative sodium transfer were then cycled at 0.18 A g-1 (per total mass of the electrodes) in the voltage range from 2.0 V to 3.8 V, demonstrating an excellent capacitance retention of 94% after 11,000 cycles. Such a remarkable life span of these NICs was ascribed to the CO2 oxidation product of the C4O42- anion, which allowed a Na2CO3 S.E.I. layer passivating very efficiently the anode surface to be formed. Hence, using Na2C4O4 shows great advantages over other sacrificial materials owing to the simultaneous simplification of the cell construction and improved properties of the NICs. Acknowledgment The authors acknowledge the financial support of the HYCAP project by the Foundation for Polish Science (research grant POIR.04.04.00-00-3D6F/16-00). References [1] X. Pan et al., Electrochim. Acta 318 (2019) 471-478. [2] P Jeżowski, et al., J. Mater. Chem. A 4, 32 (2016) 12609-12615. [3] D. Shanmukaraj et al., Electrochem. Commun. 12 (2010) 1344-1347. [4] M. S. Park et al., Adv. Energy Mater. 1 (2011) 1002-1006.

Authors : E. Genç *(1), S.Libraro (1), A. Morisset (1), M.J. Lehmann (1), A. Ingenito (2), F.J. Haug (1), C. Ballif (1) (2)
Affiliations : (1) École Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin Film Electronics Laboratory (PV-LAB), Switzerland. (2) CSEM PV-Center, Switzerland.

Resume : Cubic silicon carbide (3C-SiC) is a promising material for passivating contacts with low parasitic absorption as demonstrated in ref [1] for films deposited by hot wire chemical vapour deposition (HWCVD). In this contribution, we investigate the deposition with the more common plasma enhanced CVD using MMS as precursor gas on crystalline Si wafers covered with a passivating layer of SiO2. We studied the impact of the discharge parameters (e.g. plasma power, frequency, substrate temperature, gas flows) on the layer properties and we investigated the effect of thermal treatments similar to the ones in the current solar cell manufacturing. From ellipsometry and X-ray reflectivity we conclude that dense layers require discharge conditions with a high density of H radicals. These are obtained for a high H content in the plasma and for the combination of high discharge power and frequency. Based on the obtained results, we propose a model similar to the selective etching model used for poly-Si growth by PECVD. Annealing between 850 and 900 °C promotes the formation of nanocrystalline domains in the layer, X-Ray diffraction suggests a size of 1.5 to 2 nm. Preliminary results on surface passivation suggest the need of a buffer layer to protect the interfacial oxide against damage by the H-rich plasma. [1] Köhler, M., Pomaska, M., Procel, P. et al. A silicon carbide-based highly transparent passivating contact for crystalline silicon solar cells approaching efficiencies of 24%. Nat Energy 6, 529–537 (2021).

Authors : George Alexandru Nemnes (1,2), Nicolae Filipoiu (1), Tudor Luca Mitran (1), Sarah Derbali (3), Florentina Neatu (3), Andrei Tomulescu (3), Cristina Besleaga (3), Anca G. Mirea (3), Stefan Neatu (3), Ioana Vlaicu (3), Mihaela Florea (3), Ioana Pintilie (3)
Affiliations : (1) Horia Hulubei National Institute for Physics and Nuclear Engineering, 077126 Magurele-Ilfov, Romania. (2) University of Bucharest, Faculty of Physics, 077125 Magurele-Ilfov, Romania. (3) National Institute of Materials Physics, Magurele 077125, Ilfov, Romania.

Resume : The search for optimal light absorbers based on halide perovskite materials expanded significantly since the synthesis of 2D-3D perovskites. Incorporating larger organic cations brings several advantages, such as introducing hydrophobic moieties, thus enhancing the chemical stability [1]. Also, increasing the size of the cations their mobility is reduced, which can be used to mitigate hysteretic effects in perovskite solar cells. Given a wide range of organic cations which can be incorporated, systematic studies are required for assessing both opto-electronic and stability properties. Here, we investigate the class of 2D halide perovskites of formula A'(2)A(n-1)B(n)X(3n 1), where A' and A are the alkyl-ammonium (e.g. up to penthyl- and hexylammonium) and methylammonium cations, respectively, and X = I, Br, Cl. Several compositions are investigated first by ab initio density functional theory calculations and the most promising candidates are synthesized, followed by optical and structural (XRD) characterizations. Using DFT simulations we perform an analysis regarding the optimal absorption and the stability properties based on the calculation of formation energies. In addition, we perform stability tests, by monitoring the structural changes following finite temperature treatments. [1] A.G. Tomulescu et al., Sol. Energy Mater. Sol. Cells 227, 111096 (2021) Acknowledgement: This work was supported by a grant of the Romanian Ministry of Education and Research, CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED-2019-1567, within PNCDI III and has received funding from the EEA Grants 2014-2021, under Project contract no. 36/2021.

Authors : R.S. Costa12, A.L. Pires2, A.M. Pereira2, C. Pereira1
Affiliations : 1REQUIMTE/LAQV, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Porto, Portugal; 2IFIMUP, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Porto, Portugal;

Resume : The Era of the IoT and the paradigm of Sustainable Energy boosted the search for self-powered devices that harvest and store energy to satisfy the electrical needs of the generation of autonomous wearable electronics.1,2 Thermally-chargeable supercapacitors are a clean energy technology that is able to convert the waste thermal energy into electrical energy (as a power source) and, simultaneously, store that energy (as an energy storage system). These hybrid devices allow converting the waste thermal energy provided from low-grade heat sources (e.g., human body) into electrical energy by a thermally-induced migration of electrolyte ions towards the device electrodes based on the Soret effect.1–3 Herein, we report on the fabrication of a thermally-chargeable textile supercapacitor (TCTSC) composed of two multiwalled carbon nanotube-coated cotton electrodes (MWCNT@cotton) and an all-solid-state ionic polyelectrolyte (PVA/H3PO4). The MWCNT@cotton electrodes were prepared by directly coating the cotton substrates with a MWCNTs dispersion through a scalable textile industry process. The ionic conductivity of PVA/H3PO4 electrolyte was tuned by doping the PVA matrix with different wt% of H3PO4, unveiling an ionic conductivity value of 39 mS/cm for a PVA/H3PO4 ratio of 1:1 (m/m). The TCTSC was fabricated by sandwiching the ionic electrolyte between the MWCNTs/cotton electrodes. The thermally-induced power generation of the TCTSC was evaluated, reaching a Soret coefficient of ~2 mV/K (up to 30 mV for an applied temperature gradient of 25 K). Concerning the energy storage features, the TCTSC presented an electric double-layer charge storage mechanism, affording a working voltage of 2.27 V and an energy density of 4.33 Wh/kg at a power density of 620 W/kg. The high flexibility and the efficient performance of the TCTSC, combined with the scalable and cost-effective fabrication process, make this device a feasible solution to satisfy the challenges of autonomous wearable electronics. Acknowledgements: This work was funded by FEDER – European Regional Development Fund through COMPETE 2020 – Operational Programme for Competitiveness and Internationalization (POCI) and by Portuguese funds through Fundação para a Ciência e a Tecnologia (FCT)/MCTES under Program PT2020 in the framework of the projects PTDC/CTM-TEX/31271/2017 and NORTE-01-0145-FEDER-022096. This work was also funded by projects UIDB/50006/2020 and UIDB/04968/2020 through FCT/MCTES. R.S.C. thanks the MSc. grant funding from FEDER through project POCI-01-0247-FEDER-039833. A.L.P. thanks the junior researcher contract funded by European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 863307 (H2020-FETOPEN-2018-2019-2020-01). C.P. thanks FCT for FCT Investigator contract IF/01080/2015. 1X. Pu et al., Chem. Sci. 2021, 12 (1), 34–49. 2A.L. Pires et. al., ACS Appl. Electron. Mater. 2021, 3 (2), 696–703. 3M. Falk et al., Biosens. Bioelectron. 2019, 126 (July 2018), 275–291.

Authors : Abdyldayeva N.Y., Nussupov K.Kh., Beisenkhanov N.B.*, Bakranova D.I., Sultanov A.T., Keiinbay S.
Affiliations : Kazakh-British Technical University

Resume : The amount of solar energy reaching the Earth exceeds the energy of all the world's reserves of non-renewable energy sources. The potential of solar energy is so great that the part of it that comes to Earth in one minute is enough to meet the current energy needs of mankind for a whole year [1]. The main barrier preventing widespread use of solar cells is the high cost of the generated electricity. A promising direction for reducing the cost of photovoltaic electricity is the development of technology for silicon solar cells having various antireflecting and passivation layers [2]. The production of solar cells based on mono- and polycrystalline silicon is 83% of the total cell production. Much of the work is currently devoted to reducing the reflection of incident light, which is almost 40% in traditional silicon wafers [2]. The creation of chemically textured Si pyramids makes it possible to additionally capture and absorb the energy of the solar spectrum due to diffuse scattering of light [3]. The proper selection of a material, along with a method of cost-effective fabrication of nanostructures, is the key to improving antireflection properties and the system performance at film integration on micro-structured Si surfaces [4]. However, to obtain a surface with improved self-cleaning properties and two-level roughness, the Si pyramids must be fine-tuned further by applying a suitable film of nano-sized thickness to their textured surfaces. ZnO films with suitable thickness on textured Si surfaces not only deliver self-cleaning properties, but also serve as an anti-reflective layer, which is significant for improving the efficiency of a solar cell by reducing reflection loss. The main objectives of the given study were the theoretical calculations and experimental investigation of thin ZnO films deposited using DC magnetron sputtering of Zn target, both on the flat surface of a single-crystal Si (100) substrate and Si pyramidal structures obtained by chemical etching. ZnO films of various thicknesses have been investigated using Lumerical Finite-Difference Time-Domain (FDTD) and synthesized by magnetron sputtering at a power of 100 W and an adjustable deposition time from 300 to 1200 s. The film thickness of 70-80 nm (namely 74 nm) was found to be most suitable both theoretically and experimentally. The use of ZnO films on arrays of pyramids ranging in size from 0.5 to 1.5 microns led to a decrease in reflection to 0.08-5.42% in the wavelengths region of 300-800 nm. The synthesized ZnO films on Si pyramidal structures were investigated using X-ray reflectometry, IR spectroscopy, spectrophotometry and atomic-force microscopy (AFM). 1 Gaewdang T., Wongchaoen N. IOP Conf. Ser.: Earth Environ. Sci. 463 2020. 012074. 2 Green M.A. Prog. Photovoltaics 17 (3) 2009. 183−189. 3 Sharma D., Bhowmick S., Das A., Kanjilal A., Saini C.P. Mater. Res. Express 6 2019. 095047. 4 Yan Y.Y., Gao N., Barthlott W. Adv. Colloid Interface Sci. 169(2) 2011. 80–105.

16:00 Q&A live session / Break    
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A-9 : Rajeev Ahuja, Uppsala University
Authors : Alexandra M.I. Trefilov 1, Bogdan I. Bita 1, Sorin Vizireanu 1, Ana V. Filip 1, Marius C. Dinca 1, Bogdan A. Sava 1, Gheorghe Dinescu 1, Andreea Matei 1, Adriana Andronie 2
Affiliations : 1. National Institute for Laser, Plasma and Radiation Physics, Magurele-Ilfov, Romania 2. University of Bucharest, Physics Department, 3 Nano-SAE Research Centre, Bucharest, Romania

Resume : The cathode microporous layer (MPL), as one of the key components of the proton exchange membrane fuel cell (PEM-FC), requires specialized carbon materials to produce the two-phase flow and interfacial effects. In this respect, we designed a novel MPL based on super-hydrophobic nitrogen doped carbon nanowalls. Employing radio-frequency plasma deposition techniques directly on carbon paper we produced high quality microporous layers at competitive yield-to cost ratio with distinctive MPL properties: high porosity, good stability, considerably durability, super-hydrophobicity and substantial conductivity. Platinum-ink, serving as fuel cell (FC) catalyst, was directly sprayed on the MPLs and incorporated in the FC assembly by hot-pressing against a polymeric membrane. The integrated PEM-FCs were tested in a single cell PEM-FC on a BT-112 Single Cell Test System, showing power performance comparable to industrial quality membrane assemblies (0.33 W/cm2), with elevated working potential (0.95 V) and impeccable fuel crossover for a low-cost system resulting from a highly scalable, inexpensive, and rapid manufacturing method. Acknowledgements: This work was financially supported by UEFISCDI Romania, in the frame of the projects: PN-III-P1-1.1-PD-2019-0684 contract 106PD/2020, PN-III-P1-1.1-PD-2019-0540 contract 103PD/2020, PN-IIIP1-1.2-PCCDI-2017-0387 contract 80PCCDI/2018, PN-III-P1-1.2-PCCDI-2017-0619-contract 42PCCDI/2018, PED 271/2020, TE 205/2021 and Core Programs: PN 16N/2019 LAPLAS VII

Authors : A. Cavalli, S. Sadewasser
Affiliations : International Iberian Nanotechnology Laboratory, Portugal

Resume : Nanowires have exceptional promise for solar cell applications. Photovoltaic systems are the ideal method to harvest solar energy, but market-leading Silicon solar cells have limited potential for improvement in efficiency. The most promising class of materials is Cu(In,Ga)Se2 (CIGS): they are lighter, flexible, and significantly cheaper to produce, with a tunable direct bandgap and a high absorption coefficient in the visible spectrum. A record cell efficiency of 23.35% was demonstrated, but it is still more than 10% lower than the Shockley-Queisser theoretical performance limit (33.7%). Additionally, CIGS semiconductors contain indium, a relatively rare element. The use of nanowires (NW) as the PV absorber material can help in both these areas. In fact, they allow ~10x lower material consumption, thanks to high absorption-to-volume ratio through light-trapping, as well as an enhanced performance compared to planar layers1. It is well-known that the use of co-evaporation under vacuum is essential to obtain high-quality materials for CIGS solar cells2, thus we have focused on Molecular Beam Epitaxy deposition. By using an Al2O3 mask, we achieved position controlled growth of isolated CuInSe2 nanostructures. We are currently working on elongating the structures to obtain true 1D morphology, determining their crystalline structure by Transmission Electron Microscopy, and developing solar cell devices based on the nanostructures. 1 J.E.M. Haverkort, E.C. Garnett, and E.P.A.M. Bakkers, Applied Physics Reviews 5, 031106 (2018). 2 P. Jackson, R. Wuerz, D. Hariskos, E. Lotter, W. Witte, and M. Powalla, Physica Status Solidi (RRL) 10, 583 (2016).

Authors : Eleonora Calì,* Gwilherm Kerherve, Faris Naufal, Kalliopi Kousi, Dragos Neagu, Evangelos I. Papaioannou, Melonie P. Thomas, Beth S. Guiton, Ian S. Metcalfe, John T. S. Irvine, David J. Payne*
Affiliations : Eleonora Calì,* Gwilherm Kerherve, Faris Naufal, David J. Payne, Department of Materials, Imperial College London, London SW7 2AZ, U.K.; Kalliopi Kousi, Evangelos I. Papaioannou, Ian S. Metcalfe, School of Engineering, Newcastle upon Tyne NE1 7RU, U.K.; Dragos Neagu, Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose St, Glasgow G1 1XL, U.K.; Melonie P. Thomas, Beth S. Guiton, Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, United States; John T. S. Irvine, School of Chemistry, University of St Andrews, St. Andrews KY16 9ST, U.K.

Resume : New functional materials combining stability, resistance to degradation, and efficiency with reasonable cost and ease of synthesis are crucial for their use in renewable energy applications. In catalysis, active metal nanoparticles dispersed on oxide surfaces are of fundamental interest to overcome the use of bulk noble metals. However, these bear the substantial limitations of the conventionally employed “top-down” deposition techniques, resulting in loss of activity and performance during operation. Exsolution, i.e. metal atoms that, in a reducing environment, segregate to the surface from sites within a host oxide lattice to generate anchored nanoparticles, has proven a successful strategy to overcome such issues. However, many questions remain regarding their growth mechanism and the crystal structure evolution of the host during the reduction process. Here, the SrTiO3 perovskite has been doped with iridium (∼0.5 wt. %) at the B-site and subjected to reducing conditions required for exsolution. Ex situ characterization with a range of techniques including XRD, XPS, SEM, HR-TEM, and STEM–EDX showed that iridium metal nanoparticles are grown on the STO surface with the unique characteristic of “socketing” to the host lattice. In situ TEM studies allowed to monitor in real time nanoparticle exsolution, enabling us to deepen our understanding on the mechanistic steps involved, and to gain insights in the crystallographic behaviour of both the host lattice and the exsolved nanoparticles at the atomic scale, which is of fundamental importance in order to tailor materials design for better reactivity. The exsolved materials were tested for emission control (CO oxidation) catalysis, for which they approached 100% conversion at 450 °C. When benchmarked against a commercially available material (1% Ir/Al2O3), the exsolved samples showed a more gradual increase in activity with temperature as compared to the commercial reference sample, and also as compared to similar noble metal systems in the literature. Nevertheless, the exsolved samples showed high activity despite having nominally only half the noble metal loading (0.5% Ir-SrTiO3). Overall, this work provides a novel structure where the design of Ir-based perovskites with an extremely low noble metal amount (∼0.5% weight) is made possible by Ir incorporation in the lattice, subsequently exsolved as metallic NPs. These are reported to display catalytic activity for the CO oxidation reaction when compared to the unreduced 0.5% Ir-STO material, demonstrating that the emerged nanoparticles are responsible for the catalytic activity of this material. Overall, the distinctive socketing between the metal catalyst and the STO support, and the performance of the 0.5% Ir-doped STO reported here show promise for this material to be tested for other catalytic applications, such as water splitting, electro- catalysis for OER, and reforming reactions for syngas and/or hydrogen production.

Authors : Tsz Hin Edmund Chan Steven Hepplestone
Affiliations : University of Exeter, UK

Resume : Hybrid perovskite solar cells (with chemical formula ABX3) are of great interest due to the recently measured power conversion efficiency of greater than 25% (but theoretically, 33.7%). Perovskite structures are easily customisable, with a range of options for A, B and X. This enables us to both tune the electronic band gap and the stability by varying the composition. Two promising perovskites are the CH3NH3PbI3 (MAPI) and CH(NH2)2PbBr3 (FAPB) structures. By varying the ratio of FA and MA and doping with Br, we can potentially tune the band gap and effective masses (and hence electronic transport). In order to compromise for a more desirable bandgap for stand-alone PV and better structural stability, the hybrid perovskite constituents are then strategically layered into superlattice form. We explore the bulk properties and interfacial engineering to improve the material’s electronic transport. We present a theoretical investigation of the structural and electronic properties of MAPI(x)/FAPB(y) superlattice, performed using first–principles density functional theory and temperature dependent vibrational entropy correction. Our results show that dominating number of layers of FAPB over MAPI will decrease the band gap. We discuss why the formation energies of superlattice in hexagonal and cubic phases differ across temperature and contradicts from the ones of its ground-state constituents. The solutions will be suggested for experimental validation.

Authors : G. Mineo1,2; S. Mirabella1,2; E. Bruno1,2;
Affiliations : 1 Dipartimento di Fisica e Astronomia “Ettore Majorana”, Università di Catania, via S. Sofia 64, 95123 Catania, Italy; 2 CNR-IMM, Università di Catania, via S. Sofia 64, 95123 Catania, Italy;

Resume : Given the wide capability of small positive ions (H+ and Li+) intercalation, WO3 represents a promising material for energy storage applications. In this scenario, nanostructured WO3 is extremely interesting due to its high surface-to-volume ratio allowing a high rate of charge transfer in supercapacitors with hexagonal crystal structure confirmed by XRD investigation and drop coated onto an appropriate substrate. Growth optimization against time, pH and temperature of synthesis allowed to get a stable morphology. A large electrochemical study (employing by cyclic voltammetry, electrochemical impedance spectrometry and galvanostatic charge discharge analysis) allowed to study firstly the mass dependence of electrochemical properties and then allowed to measure quantitative performances of WO3 nanorods in terms of specific capacitance (Cs). These data are presented and discussed.

Authors : Pablo Jimenéz-Calvo 1*, Mario J. Muñoz-Batista 2, Gilberto Teobaldi 3,4,5, Erwan 1*
Affiliations : 1 Solid-State Physics Laboratory, University of Paris-Saclay, CNRS, 91405, Orsay, France 2 Department of Chemical Engineering, Faculty of Sciences, University of Granada, Avda. Fuentenueva, s/n 18071, Granada, Spain 3 Scientific Computing Department, STFC UKRI, Rutherford Appleton Laboratory, Harwell Campus, OX11 0QX Didcot, United Kingdom 4 Stephenson Institute for Renewable Energy, Department of Chemistry, University of Liverpool, L69 3BX Liverpool, United Kingdom 5 School of Chemistry, University of Southampton, Highfield, SO17 1BJ Southampton, United Kingdom

Resume : Solar energy is a potential avenue to mitigate several planet crises, such energy supply and production. Global population is reaching ≈ 9 billion for 2050, with an expected electricity consumption of 28 TW. Therefore, harvesting and storing solar energy is regarded as a suitable solution for the energy crisis.1 Photocatalysis as a state-of-the-art technology has exhibited reasonable harvesting of solar energy, allowing chemical transformations to generate solar fuels, such as hydrogen (H2), a key vector for the foreseen low-carbon economy due to its high energetic density ca. 142 MJ/kg.2 A single catalyst exhibiting an efficient solar-to-photon conversion remains as the bottleneck for further technological development.3 Despite of using benchmark semiconductors (SCs), such as Titanium dioxide (TiO2) still do not surpass the needed efficient conversion. TiO2 limitations are described as water oxidation overpotential, large band gap i.e., 3.2 eV, and only UV light absorption. Thus, adding a metal (M) onto a SC, as TiO2, creates an interesting Schottky junction, regarded as one state-of-the-art approach in Materials Science to enhanced solar energy conversions. One relevant feature on the new interphase junction is the expected enhancement of SCs photoactivities in the order of 10-100 folds than the SC efficiency alone.4 Remarkably, the materials design aims at increasing the limited light absorption of TiO2 by plasmonic effects, to create an intimate M/SC interphase contact to promote new electronic paths and increase the amount of co-catalytic sites along the support surface.5 In this work, two scientific contributions are in evidence. The Schottky materials’ strategy and a new gas tight photochemical cell reactor. The latter was developed for acquiring accurate H2 photoproduction and to correlate the physico-chemical properties of the formed Schottky junctions with their activity. The as-synthesized composites (M/ TiO2, M: Pd. Pt, and Au) with varied M loading 0.5, 1, and 2 wt.% were characterized by X-ray scattering, Transmission electron microscopy, Infrared, UV-vis, Ultraviolet / X-ray photoelectron spectroscopies and Inductively coupled plasma. The ICP results confirm the expected M loadings, thanks to the controlled two-pot M reduction/deposition method. TEM results exhibited average M NPs sizes from 2 to 5 nm. Moreover, the photocatalytic H2 production was quantified over time, exhibiting rates of 13, 10, and 7 mmol h-1 gcat-1 for the highest loading, e.g., 2wt.% (Pd, Pt, Au)/TiO2, respectively, after 3h of irradiation. Correlations between structure, M loadings, distribution-size-coverage of M NPs, and the photocatalytic factors (quantum yield & H2 photoproduction) will be discussed. Also, a 2D photonic profile is provided for the new photoreactor. Acknowledgements The authors thank the French ANR agency for financial support (grant N° ANR-18-CE09-0001, C3PO) and CNRS through International Emerging Actions program (grant N° 08216). References 1. N. S. Lewis and D. G. Nocera, PNAS, 2006, 103, 15729-15735. 2. N. S. Lewis, Science, 2007, 315, 798-801. 3. M. Melchiona and P. Fornasiero, ACS Cat, 2020, 10, 10, 5493-5501. 4. Y. Dubi and Y. Sivan, Light Sci Appl, 2019, 8, 89. 5. P. Jiménez-Calvo et al., Nano Energy, 2020, 75, 104888.

10:10 Q&A live session / Break    
Authors : A.E. Lauritzen, B. Putland, T. Derrien, I. A. Habib, A. Jungbluth, P. Kaienburg, R. Dalgliesh, M. Riede
Affiliations : University of Oxford, University of Oxford, University of Exeter, Diamond Light Source, University of Oxford, University of Oxford, ISIS Neutron and Muon Source, University of Oxford,

Resume : Organic solar cells (OSCs) based on organic semiconducting molecules offer the possibility of low-cost solar power generation that can be deployed on light-weight and flexible substrates. Photogenerated charge carriers in OSCs manifest as strongly bound electron-hole pairs which must diffuse to an interface in the two-component active layers to be efficiently separated before they recombine. Given the current exciton diffusion lengths, this requires phase-separated domains on the order of ~100 Å to ensure efficient charge dissociation, with suboptimal morphology being a hindrance to commercialisation. Small Angle Neutron Scattering (SANS) can probe the microstructure at such length scales and has been used extensively to study the morphology of polymer OSCs [1], due to the natural scattering contrast between the hydrogen-rich polymers and the carbon-rich fullerenes. However, SANS has yet to be used to characterise the morphology of OSCs based on evaporated small molecule solar cells. In this work, we employ SANS at the ISIS Muon & Neutron Source to study the morphology/microstructure of active layers of evaporated OSCs for the first time. We investigate bulk heterojunctions manufactured under different fabrication conditions, such as different molecular ratios between the electron donor and acceptor moieties, evaporation rates, and varied substrate temperatures during deposition. Various donor molecules, such as alpha-sexithiophene, methylated DCV5T, zinc phthalocyanine, and rubrene, in conjunction with the fullerene C60 are investigated. Our results show how SANS can be used to qualitatively describe the phase mixing behaviour of different blends, such as whether the donor:acceptor system is fully mixed, weakly separating, or shows a distinct two-phase system [2], such as DCV5T spheres in a C60 matrix. These results are verified using Scanning Transmission Electron Microscopy with Energy Dispersive X-ray (STEM-EDX). In addition, we use SANS model fits to quantitatively describe changes in the morphology as growth conditions are varied and link these changes to OSC device performance, demonstrating how SANS can be used to develop key structure-property relationships of evaporated OSCs. [1] Y. Wen and M. Dadmun, "A new model for the morphology of P3HT/PCBM organic photovoltaics from small-angle neutron scattering: rivers and streams." ACS nano 5.6 (2011): 4756-4768. [2] A. Guinier and G. Fournet, ⤜Small-Angle Scattering of X-Rays⤝, John Wiley and Sons, New York, (1955)

Authors : Arianna Melillo (1), María Cabrero Antonino (1), Belén Ferrer (1), Herme G. Baldoví (1) Sergio Navalón (1).
Affiliations : (1) Department of Chemistry Universitat Politècnica de Valencia, Spain

Resume : Metal-organic frameworks (MOFs) are a class of crystalline porous materials constituted by metal ions or metal clusters coordinated to organic ligands.[1] Due to their high tunability and flexibility MOFs have found application in many areas. In particular, MOFs are envisioned as promising candidates for the solar-driven production of solar fuels.[2] In fact, many studies have reported the use of MOFs as photocatalysts for H2 generation from water using sacrificial agents. One of the most studied MOFs as photocatalysts is UiO-66(Zr) (Universitetet i Oslo). UiO-66(Zr) is constituted by Zr-oxo clusters coordinated to 1,4-benzenedicarboxylates having an ideal formula Zr6O4(OH)4(OOC-C6H4-COO)6. Theoretical and experimental evidences have demonstrated that the introduction of Ce4+ or Ti4+ ions in the metal cluster of UiO-66(Zr) facilitates the ligand-to-metal charge transfer (LMCT) mechanism from the organic ligand to the metal cluster and, therefore, its resulting photoactivity.[2,3] More recently, our group and others have reported the possibility of using MOFs as photocatalyst for the photocatalytic overall water splitting (OWS) into H2 and O2 in the absence of sacrificial agents.[4,5] In this work we report for the first time the preparation of a trimetallic UiO-66(Zr/Ce/Ti) with superior activity respect to their mono- or bimetallic MOFs for the photocatalytic OWS under UV-Vis or visible light irradiation.[6] In particular, the UiO-66(Zr/Ce/Ti) photocatalyst can achieve 210 μmol ∙ g−1 of H2 and 70 μ mol ∙ g−1 of O2, under visible light irradiation. Fluorescence and time-resolved absorption spectroscopies were employed to show favorable charge separation efficiency when using the trimetallic UiO-66(Zr/Ce/Ti) as photocatalyst.

Authors : Soranyel Gonzalez-Carrero, Jan Kosco, Michael Sachs, Teng Fei, Zhang Chen, Yifan Dong, Xu Weidong, Iain McCulloch, James Durrant
Affiliations : Soranyel Gonzalez-Carrero; Michael Sachs; Teng Fei; Zhang Chen ; Dong Yifan ; Xu Weidong; James Durrant Department of Chemistry, Centre for Processable Electronics, Imperial College London, London W12 0BZ, U.K. Jan Kosco; Iain McCulloch Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Oxford, UK Department of Physical Sciences and Engineering, KAUST Solar Centre (KSC), Saudi Arabia, Saudi Arabia

Resume : Carbon-based materials and organic semiconductor nanoparticles are promising for use as low-cost and efficient photocatalyst materials, mainly due to the easy tunability of their properties through synthetic control, which allow the design of materials with tuned opto-electronic properties by incorporating different building blocks.1,2 The best performing systems are bulk heterojunctions nanoparticles prepared from a blend of polymers donor and non-fullerene small molecules acceptor, particularly due to their improved light absorption in the visible range.3 Despite the efficient performance of the donor/acceptor bulk heterojunction photocatalysts for hydrogen evolution, the fundamental understanding of the photophysical processes that determine their performance remain limited.2 In this presentation, I will introduce our recent spectroscopic studies of a series of donor/acceptor bulk heterojunction photocatalysts with different hydrogen evolution activity, including the highest performing donor/acceptor bulk heterojunction nanoparticles photocatalysts reported to date. Transient absorption spectroscopy, on timescales of femtoseconds to milliseconds after light absorption, was used to explore the charge carrier dynamics of bulk heterojunction nanoparticles and their correlation with photocatalytic performance. I will discuss the similarities and differences between the function of such donor/acceptor bulk heterojunction photocatalysts and single conjugated polymers photocatalyst. These results can provide insight into the design requirement for optimum function of organic semiconductors photocatalysts for solar-to-fuel conversion. References. 1. Wang, Y.; Vogel, A.; Sachs, M.; Sprick, R. S.; Wilbraham, L.; Moniz, S. J. A.; Godin, R.; Zwijnenburg, M. A.; Durrant, J. R.; Cooper, A. I.; Tang, J., Current understanding and challenges of solar-driven hydrogen generation using polymeric photocatalysts. Nature Energy 2019, 4 (9), 746-760. 2. Sachs, M.; Cha, H.; Kosco, J.; Aitchison, C. M.; Francàs, L.; Corby, S.; Chiang, C.-L.; Wilson, A. A.; Godin, R.; Fahey-Williams, A.; Cooper, A. I.; Sprick, R. S.; McCulloch, I.; Durrant, J. R., Tracking Charge Transfer to Residual Metal Clusters in Conjugated Polymers for Photocatalytic Hydrogen Evolution. Journal of the American Chemical Society 2020, 142 (34), 14574-14587. 3. Kosco, J.; Bidwell, M.; Cha, H.; Martin, T.; Howells, C. T.; Sachs, M.; Anjum, D. H.; Gonzalez Lopez, S.; Zou, L.; Wadsworth, A.; Zhang, W.; Zhang, L.; Tellam, J.; Sougrat, R.; Laquai, F.; DeLongchamp, D. M.; Durrant, J. R.; McCulloch, I., Enhanced photocatalytic hydrogen evolution from organic semiconductor heterojunction nanoparticles. Nature Materials 2020, 19 (5), 559-565.

Authors : Julian Martin, Julia Melke, Anna Fischer
Affiliations : 1 Institute of Inorganic and Analytical Chemistry, University of Freiburg, Freiburg, Germany 2 Freiburg Materials and Research Center, Freiburg, Germany; 1 Institute of Inorganic and Analytical Chemistry, University of Freiburg, Freiburg, Germany 2 Freiburg Materials and Research Center, Freiburg, Germany; 1 Institute of Inorganic and Analytical Chemistry, University of Freiburg, Freiburg, Germany 2 Freiburg Materials and Research Center, Freiburg, Germany 3 Freiburg Center for Interactive Materials and Bioinspired Technologies, Freiburg, Germany 4 Cluster of Excellence livMatS @ FIT – Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Freiburg Germany

Resume : In commercial polymer electrolyte fuel cells platinum(-alloys), supported on conductive carbon materials, catalyze the hydrogen oxidation (anodic process) and the oxygen reduction reaction (ORR) (cathodic process). Thereby, carbon materials play a crucial role, e.g. as catalyst support. The platinum/carbon catalyst system still can be optimized towards its activity for the ORR and, more importantly towards long-term stability. Indeed, electrochemically active surface area is lost during operation by Pt particle detachment and/or carbon corrosion [1]. To overcome these degradation processes, the carbon support can be modified by advantageous nanostructuring to achieve high Pt dispersion and/or by incorporation of nitrogen functionalities as anchoring groups for platinum [2]. Mesoporous N-doped carbon materials (N-HTC) obtained by hydrothermal carbonization from biomass derived precursors were developed and used as support for Pt nanoparticles [3]. By temperature treatments the N-content and graphitization of the N-HTC supports can be adjusted [4]. Platinum nanoparticle deposition on the various N-HTC supports was achieved by wetness impregnation and thermal reduction of a platinum salt precursor. The influence of the synthesis conditions and as such of the support and nanoparticle properties on the ORR activity and stability of the developed catalysts was investigated by electrochemical rotating disk electrode (RDE). The optimized Pt/N-HTC ORR catalyst showed higher stability (over 10000 AST cycles) when compared to a commercial Pt/C catalyst. [1] J.C. Meier, C. Galeano, I. Katsounaros, J. Witte, K.J.J. Mayrhofer, Beilstein J. Nanotech 5 (2014), 44–67. [2] J. Melke, R. Schuster, S. Möbus, T. Jurzinsky, P. Elsässer, A. Heilemann, A. Fischer, Carbon 146 (2019) 44–59. [3] J. Martin, J. Melke, C. Njel, A. Schökel, J. Büttner, A. Fischer, 2021, to be submitted. [4] J. Melke, J. Martin, M. Bruns, P. Hügenell, A. Schökel, S. M. Isaza, F. Fink, P. Elsässer, A. Fischer, ACS Appl. Energy Mater. 3, 12 (2020) 11627-11640.

Authors : Sang Rim Shin, Hae Sung Cho, Yongjin Lee, Suji Gim, Jeung Ku Kang
Affiliations : Department of Materials Science & Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yeseong-gu, Daejeon 305-701, Republic of Korea; School of Physical Science and Technology, ShanghaiTech University, Shanghai, China; Department of Chemical Engineering, Inha University, Incheon, Republic of Korea

Resume : With the recent growing interest in the environment and energy, the demands for green energy having a low carbon footprint are increasing. To make a breakthrough in these challenges, the development of material to control the gas molecules is crucial. Especially, understanding the gas adsorption behavior in porous materials is necessary for catalysis and gas storage applications. One of the best conventional analysis methods to characterize it is adsorption isotherm. However, if it is used alone, it is difficult to locate or identify the behavior of the adsorbate molecules. Herein we report CO2 behavior of early adsorption stages in MIL-101 (Cr, Fe, and V), by simultaneous analysis of their adsorption isotherms and X-ray diffraction patterns. Each adsorption isotherm shows unique characteristics; this was analyzed by the interaction between the adsorbate and the corresponding framework using the CO2 distribution map in the pores, electron paramagnetic resonance spectroscopy, and DFT simulation results. Notably, the CO2 isotherm shape for V-MIL-101 is convex at the very early stage and then becomes concave to the p/po axis, until the pore condensation starts. For Fe-MIL-101, the overall isotherm slope is relatively linear during the stage. Cr-MIL-101, which shows the highest CO2 uptake among the samples, has a concave-shaped isotherm. Meanwhile, Ar isotherms show similar profiles throughout the adsorption pressure range regardless of the metals. Their continuous adsorption processes before pore condensation are visualized as accumulated CO2 distribution maps based on in-situ X-ray diffraction. We can infer that Cr-MIL-101 has strong framework-adsorbate interaction and hence, high CO2 uptake in the initial adsorption stage, represented by the concave isotherm shape. The monolayer adsorption gradient changed greatly depending on the metal-CO2 attraction force. However, after CO2 adsorption and layer formation, the CO2-CO2 forces can promote the adsorption of more molecules thereby, making the isotherm of V-MIL-101 convex. Furthermore, under the CO2 atmosphere, the electron paramagnetic resonance intensity of MIL-101s, which is proportional to the number of unpaired electrons, decreased in all three materials significantly. These results indicate that though the three metals contain unpaired electrons, and their respective interactions with CO2 are explained with their d orbital configurations. Also, the adsorption energy values derived by the DFT calculation show that the trend of intermolecular interaction is in order of Cr >> Fe > V, consistent with the experimental results. Through this research, we can gain additional insights into the adsorbate distribution within pores during the gas adsorption process and the comprehensive adsorbate behaviors in the different pore environments. This approach can contribute to explaining adsorption mechanisms and construction guidelines for porous materials in gas-storage and catalysis industries.

Authors : Li-chung Kin, Oleksandr Astakhov, Minoh Lee, Stefan Haas,Uwe Rau,, Tsvetelina Merdzhanova
Affiliations : IEK5 – Photovoltaik, Forschungszentrum Jülich GmbH, Jülich, 52425 Germany

Resume : Solar based hydrogen power is promising as a renewable fuel that can be generated anywhere there is sunshine and water. Many attempts have been made to integrate a water electrolyser and solar cell into one seamless package (a so-called artificial leaf) to take advantage of the cooling provided by the water to the solar cell, reduced losses from the lack of wiring and the increased portability afforded by an integrated unit 1. However, in literature, much less attention is payed to the need for a minimum current across the electrolyser under insufficient illumination to prevent excessive catalyst degradation and dissolution2. Attaching an appropriately sized, voltage matched battery to an artificial leaf could address this need and in theory could also increase efficiency of the setup across one diurnal cycle. We experimentally show that this can be achieved without any power electronics and, as is theorized, the presence of the battery also has a positive effect on the operation of the electrolyser and improves solar-to-hydrogen efficiency by reducing the current density across the electrolyser. A 7 cell silicon heterojunction module , two bifunctional NiFeMo electrolysers in series and a commercial Li-ion NMC battery were selected to provide the same amount of solar output power despite different working voltages and tested in a series of simulated diurnal cycles. The increased average solar to hydrogen efficiency per cycle (11.4% vs 10.5% without the battery) is analyzed and discussed with implications for future integrated artificial leaf design and implementation. 1. M. Lee, B. Turan, J.-P. Becker, K. Welter, B. Klingebiel, E. Neumann, Y. J. Sohn, T. Merdzhanova, T. Kirchartz, F. Finger, U. Rau and S. Haas, Advanced Sustainable Systems, 2020, 4, 2000070. 2. A. Weiß, A. Siebel, M. Bernt, T. H. Shen, V. Tileli and H. A. Gasteiger, Journal of The Electrochemical Society, 2019, 166, F487-F497.

12:45 Q&A live session / Break    
A-11 : Wei Luo, Uppsala University
Authors : Kaihu Xian, Yang Liu, Yanhou Geng, and Long Ye
Affiliations : School of Materials Science and Engineering, Tianjin Key Laboratory of Molecular Optoelectronic Sciences, Tianjin University, Tianjin, 300350, China,

Resume : Poly (3-hexylthiophene) (P3HT) has been considered as a promising commercial organic photovoltaic (OPV) material due to its low cost and large scalability. However, the power conversion efficiency (PCE) of current P3HT-based OPV cells is too low to meet the requirements of practical applications. In this work, we select the high-efficiency P3HT:ZY-4Cl blend as a model system to reveal the time-dependent evolution of crystallization, morphology and photovoltaic performance of the system during thermal annealing process. It was found that the amorphous acceptor crystallized/aggregated rapidly with the extension of annealing time, while the crystallinity of P3HT enhanced slightly but did not change visibly before and after annealing. Therefore, the phase separation of the device blends increases gradually with the annealing time prolonging, so that the device efficiency increases rapidly at first and then decreases slowly. We achieved an impressive PCE of more than 10% after only thermal annealing for 30 seconds at 130 ?, which is the highest efficiency of P3HT-based OPV. This is significantly higher than the efficiency of conventional annealing for 10 min (9.3%) and approximately 20 times that of as cast devices (0.5%). This work suggest that delicate control of both donor and acceptor crystallinity is crucial to the performance optimization of P3HT-based OPVs.

Authors : Joana S. Teixeira1,2, André M. Pereira2, Clara Pereira1
Affiliations : 1 REQUIMTE/LAQV, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto (FCUP), Portugal. 2 IFIMUP, Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, FCUP, Portugal.

Resume : The evolution of smart electronics resulted in a movement towards real-time sensing and a web-connected society, leading to the rapid development of e-textiles. The extensive use of wearable technologies boosted the development of energy storage textiles that charge faster and store energy for longer time.[1,2] Additionally, the multifunctionality of textiles is also an important aspect to create high value-added products.[3] Herein, a novel dual-functional textile supercapacitor combining enhanced energy storage and optical properties was produced. A new redox-active solid-gel electrolyte based on fluorescent manganese(II)-doped zinc(II) sulfide was for the first time used to endow multifunctionality to the device when assembled with MWCNT-based textile electrodes. The fluorescent compound was composed of sphalerite and wurtzite ZnS phases doped with Mn2 and exhibited a rhombic structure. The MWCNT-coated textile electrodes (with high electrical conductivity, 704 Ω cm-2 of electrical resistance), were prepared through a simple eco-sustainable dip-pad-dry process using a natural cotton fabric as substrate. The fluorescent hybrid textile supercapacitor exhibited 20% higher working voltage (1.64 V), 48% higher energy density (1.63 W h kg-1) and 74% higher power density (641.6 W kg-1) than the textile supercapacitor based on the undoped electrolyte. These improvements arised from a synergistically-enhanced properties that lead to a hybrid energy storage mechanism. Additionally, it presented excellent cycling stability of 100% after 8000 charge/discharge cycles. The device exhibited an intense yellow-orange fluorescence under UV light, preserving at the same time the energy storage functionality. This work opens promising perspectives on multifunctional energy storage textiles for dark environment applications, such as in reflective/safety electronic clothing for nighttime users. Acknowledgments. Funded by FEDER through COMPETE 2020-POCI and by FCT/MCTES under Program PT2020 (project PTDC/CTM-TEX/31271/2017). Work also supported by UIDB/50006/2020 and UIDB/04968/2020 with funding from FCT/MCTES through national funds. JST and CP thank FCT for PhD scholarship (SFRH/BD/145513/2019) and FCT Investigator contract IF/01080/2015, respectively. References: [1] X. Zhang, C. Jiang, J. Liang, W. Wu, Electrode materials and device architecture strategies for flexible supercapacitors in wearable energy storage, J. Mater. Chem. A 9 (2021) 8099–8128. [2] R.S. Costa, A. Guedes, A.M. Pereira, C. Pereira, Fabrication of all-solid-state textile supercapacitors based on industrial-grade multi-walled carbon nanotubes for enhanced energy storage, J. Mater. Sci. 55 (2020) 10121–10141. [3] C. Pereira, A.M. Pereira, C. Freire, T. V Pinto, R.S. Costa, J.S. Teixeira, Chap. 21 - Nanoengineered textiles: from advanced functional nanomaterials to groundbreaking high-performance clothing, in: Handb. Funct. Nanomater. Ind. Appl., Elsevier, 2020, pp. 611-714.

Authors : Paola Andrea Delcompare Rodriguez, Nicola Seriani
Affiliations : University of Trieste -The Abdus Salam International Centre for Theoretical Physics; The Abdus Salam International Centre for Theoretical Physics.

Resume : During the last decades many effort has been devoted to understand the hematite-electrolyte interface due to its potential application in photoelectrochemical water splitting. It is well known that this interface can extend over lengths ranging from tens of nanometers to micrometers, therefore its realistic simulation via ab initio-calculations has been seen as an impossible task. However, recent experiments measured space charge layers smaller than ~10 Angstrom in highly doped nanostructured hematite photoanodes displaying high photocurrent densities in water splitting experiments [1]. Using a set of continuous equations based on the based on the Poisson-Boltzmann distribution and the Stern model [2], we investigated under which experimental conditions the space charge layer in hematite becomes ultrathin. In this regime a considerable fraction of the potential drop across the interface is located in the Helmholtz layer, therefore corrections to the Mott-Shottky equation should be taken into account in this regime. These equations also allowed us to examine the effect of the macroscopic properties provided by experiments on the microscopic properties of the interface: We got access to the width of the space charge layer; and the distribution of the electrostatic potential among the space charge layer in the solid, the Helmholtz layer and diffuse layer as a function of the experimental conditions. We then used density functional theory to get an atomistic insight of the space charge layer in the semiconductor in systems ranging from the pristine stoichiometric surface, a surface with adsorbed hydroxyls to Ti-doped slabs with doping densities of the order of ~1.0E21 cm^{-3}. According to our analysis with the continuous equations, space charge layers smaller than 10 Angstrom must have been present also in other experiments with some of highest photocurrent performances registered [3]. We found that at high doping densities the inverse of the square of the capacitance should have a quadratic behaviour near the flat-band potential and a sub-linear behaviour due to square-root-like corrections far from it. We computed the band bending of the proposed atomistic models using Density functional theory. The pristine stoichiometric and the hydroxylated undoped surfaces displayed band bendings of 0.14 eV and 0.49 eV, respectively, with space charge layers extending in the sub-nanometer regime. At high doping concentrations, we observed that space charge layers in hematite thin films can become comparable with interatomic distances. Contrary to the common picture of the electrochemical interface of a semiconductor and an electrolyte, the latter results give an insight of an unexpected regime of high photoelectrocatalytic efficiency in ultrathin space charge layers, which are accesible to quantum mechanical ab-initio calculations. [1] Z. Zhang, H. Nagashima, and T. Tachikawa, Angew. Chem. Int. Edit. 59, 9047 (2020). [2] Y. V. Pleskov and Y. Y. Gurevich, Semiconductor Photoelectrochemistry, 1st ed. (Consultants Bureau, New York, 1986) [3] F. L. Formal, N. Tétreault, M. Cornuz, T. Moehl, M. Grätzel, and K. Sivula, Chem. Sci. 2, 737 (2011).

Authors : Julia Marí-Guaita, Amal Bouich, Bernabé Mari
Affiliations : Institut de Disseny i Fabricació Universitat Politècnica

Resume : Methylammonium Lead Iodide (MaPbI3) and Methylammonium Tin Iodide (MASnI3) thin absorber layers are potential candidates used as absorber layer in perovskite device. Herein, both compounds have been successfully prepared with one step spin coating technique. The prepared samples were characterized by different techniques like X-ray diffraction (XRD), atomic force microscopy (AFM), surface electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmittance electrons microscopy (TEM), UV–Visible spectroscopy and photoelectrochemical (PEC) analysis. The XRD analysis confirms the tetragonal structure of the prepared thin films. AFM analysis exposed that the MASnI3 displays better roughness (54 nm) and grain size (65 nm) than MAPbI3 which has of roughness of 30 nm and grain size of 21 nm. For both samples, SEM analysis revealed smooth and homogenous surface and large grain size and pinhole-free perovskite film. The optical absorption spectrum showed the direct bandgap of MASnI3 1.8 eV and 1.6 eV for MaPbI3 thin films. Based on the results the MASnI3 used as an absorber layer can be a good choice for an efficient photovoltaic device.

Authors : Eva Montero-Lanzuela*(1), María Cabrero-Antonino(2), Herme G. Baldoví(3) & Sergio Navalón(4)
Affiliations : (1) Departamento de Química, Universitat Politècnica de València, C/Camino de Vera, s/n, 46022 Valencia, Spain; (2) Departamento de Química, Universitat Politècnica de València, C/Camino de Vera, s/n, 46022 Valencia, Spain; (3) Departamento de Química, Universitat Politècnica de València, C/Camino de Vera, s/n, 46022 Valencia, Spain; (4) Departamento de Química, Universitat Politècnica de València, C/Camino de Vera, s/n, 46022 Valencia, Spain

Resume : There is an increasing interest in developing energy vectors alternative to the use of fossil fuels.[1] One of the most interesting approaches to obtain sustainable energy is to convert solar energy into chemical energy. Heterogeneous photocatalysis is an important approach for this purpose. However, the development of efficient solar-driven heterogeneous photocatalysts still remains a challenge. In the last decades a relatively new class of crystalline and porous materials termed as metal-organic frameworks (MOFs) has emerged as potential heterogeneous photocatalysis for the production of hydrogen using UV-Vis or visible light irradiation.[2] Most of these studies, however, employ sacrificial agents such as triethanolamine or methanol and, therefore, hampering the real application of these systems. More recently, a series of studies have reported the possibility of using MOFs as heterogeneous photocatalysts for the overall water splitting (OWS). [3,4] In the present work we report the influence of the presence of Pt, RuOx and/or CoOx NPs as co-catalyst within the MOF named as MIL-125(Ti)-NH2 with ideal formula Ti8O8(OH)4-(O2CC6H5-CO2-NH2)6 for the photocatalytic OWS.[5] The simultaneous combination of Pt and RuOx NPs within the MIL-125(Ti)-NH2 network resulted in an active photocatalyst under UV-Vis light reaching a H2 and O2 production of 218 and 85 mol/g of photocatalyst at 24 h, respectively. With this photocatalyst a maximum apparent quantum efficiency at 400 nm of 0.32 % was obtained. More importantly, the Pt/RuOx@MIL-125(Ti)-NH2 photocatalyst is active under natural sunlight irradiation achieving a H2 and O2 productions of about 28 and 14 mol g-1 in 10 h. Refs.[1] N.S. Lewis, Introduction: Solar Energy Conversion, Chem. Rev, 115 (2015) 12631-12632. [2] A. Dhakshinamoorthy, Z. Li, H. Garcia, Catalysis and photocatalysis by metal organic frameworks Chem. Soc. Rev., 47 (2018) 8134-8172.[3] Y. An, Y. Liu, P. An, J. Dong, B. Xu, Y. Dai, X. Qin, X. Zhang, M.-H. Whangbo, B. Huang, NiII Coordination to Al-Based Metal–Organic Framework Made from 2-Aminoterephthalate for Photocatalytic Overall Water Splitting, Angew. Chem. Int. Ed., 56 (2017) 3036 –3040. [4] A. Melillo, M. Cabrero-Antonino, S. Navalón, B. Ferrer, H. García, Enhancing visible-light photocatalytic activity for overall water splitting in UiO-66 by controlling metal node composition. [5] S. Remiro-Buenamañana; M. Cabrero-Antonino; M. Martínez-Guanter; M. Álvaro; S. Navalón; H. García. Influence of co-catalysts on the photocatalytic activity of MIL-125(Ti)-NH2 in the H. water splitting. Clave A, Appl. Catal. B. Environ. 254, 677-684, 2019.

Authors : Gamze Atak,Sagar Ghorai, Claes G. Granqvist, Gunnar A. Niklasson, İlknur Bayrak Pehlivan.
Affiliations : Gamze Atak1,2; Sagar Ghorai1; Claes G. Granqvist1; Gunnar A. Niklasson1; İlknur Bayrak Pehlivan. 1Department of Materials Science and Engineering, Ångström Laboratory, Uppsala University, P.O. Box 35, SE-751 03 Uppsala, Sweden 2Hacettepe University, Department of Physics Engineering, 06800 Beytepe, Ankara, Turkey

Resume : Materials that can change their optical properties as a response to an external electrical voltage are referred to as “electrochromic.” The materials’ coloration is denoted “cathodic” under ion insertion and “anodic” under ion extraction. Conventionally, electrochromic (EC) device structures have five superimposed layers: transparent conducting oxide (TCO) layer / cathodic EC layer / ion-conducting layer / anodic EC layer / TCO layer, either all on one substrate or positioned between two substrates in a laminated configuration. Ion conducting layers (electrolytes) play a vital role in the operation of EC systems. They should provide high ion conductivity and transparency, low electronic conductivity, and compatibility with both anode and cathode. In this work, we prepared W oxide thin films by reactive DC magnetron sputtering and investigated their electrochromic properties, durability, and potentiostatic rejuvenation in LiClO4-propylene carbonate electrolytes containing up to 3.0 wt% of SiO2 nanoparticles with a diameter of 7 nm. The effect of adding nanoparticles to the electrolyte on ionic conductivity, chemical state, and morphological structure of the thin films was examined. The addition of 1.0 wt% SiO2 in the electrolyte led to high charge capacity and optical modulation in the W oxide films. A significant improvement in durability during voltammetric cycling was observed in the commonly used potential range of 2.0–4.0 V as well as under harsh conditions, which correspond to the range 1.5–4.0 V.

Authors : M. Zubkins, I. Aulika, E. Strods, V. Vibornijs, L. Bikse, J. Purans
Affiliations : Institute of Solid State Physics, University of Latvia, Kengaraga 8, LV-1063, Riga, Latvia

Resume : Yttrium and other rare-earth (RE) metal oxy-hydrides (YHO, REHO – notations referred in the text hereinafter, in principle, is irrespective to the stoichiometry) are a new class of inorganic mixed-anion materials [1], which exhibit a photochromic effect and a light-induced resistivity change at room temperature and ambient pressure. These switchable optical and electrical properties enable their utilization in a multitude of technological applications, such as energy-saving smart windows, sensors, ophthalmic lenses, and medical devices. Recently reported studies show that the modification of the deposition parameters causes significant changes in the composition of REHO films, accompanied by a varying optical properties. In order to tune and fully exploit REHOs in applications, further progress requires: reaction conditions for film synthesis have to be investigated carefully, including the film oxidation kinetics and the characterization of the oxy-hydride phase. In this work, the films were fabricated on soda-lime glass using the vacuum PVD coater G500M (Sidrabe Vacuum, Ltd.) at various sputtering pressure (SP) from 3 mTorr up to 20 mTorr. Detailed characterisations by profilometer CART Veeco Dektak 150, X-ray diffractometer with Cu Kα radiation, Rigaku MiniFlex 600, high-resolution dual-beam scanning electron microscope Thermo Scientific Helios 5 UX, and spectroscopic ellipsometer WOOLLAM RC2 were performed. For the first time in-situ oxidation dynamics were observed by means of the transmittance measurements just after the deposition of the films by introducing the oxygen in the sputtering chamber. Transmittance increases and oxidation time constant rapidly decreases with increase of the film SP. XRD analysis show that the crystallographic structure of the film is just slightly affected by the SP: with increase of the SP the intensity of the peak around 29 degrees of 2-theta is decreasing thus films undergo compositional changes rather than structural. The SP of approximately 6.0-6.5 mTorr was found to be a critical pressure, where the refractive index n extinction coefficient k dispersion curves completely change the characteristic from metallic to semiconductor/dielectric behavior with Tauc optical band Eg around (2.5-2.8) eV. Moreover, all films fabricated at SP higher than this critical pressure exhibit optical gradient: n decreases in direction from the bottom to the top of the films, and the lower is the SP, the higher is the n difference within the depth of the films. For all films, the Eg and n increases and k decreases with increase of SP. ACKNOWLEDGMENTS This research is supported by the Horizon 2020 Project CAMART² under grant agreement No 739508 and national project “Thin films of rare-earth oxy-hydrides for photochromic applications” FLPP No LZP-2020/2-0291. [1] Kageyama, Hiroshi, et al., Nature communications 9.1 (2018): 1-15.

15:45 Q&A live session / Closing Remarks    

Symposium organizers
Priya VASHISHTAUniversity of Southern California

Dept. of Physics & Astronomy, Los Angeles, CA 90089-0242, USA
Rajeev AHUJA (Main Organizer)Department of Physics and Astronomy, Uppsala University

Box-516 SE-75120 Uppsala, Sweden
Yong-Mook KANGKorea University

Dept. of Materials Science and Engineering - 145 Anam-ro, Seongbuk-gu, Seoul, 02841, Korea